The USSR could not survive inevitably, as I assume all authoritarian regimes cannot survive in the long-term due to eventual popular action. Furthermore, one cannot use the idea of 'economic reforms' to create a USSR that stretches into the 21st century, in which all the problems associated with the country are taken away through certain developments. The PRC has established a precedent, yes, along with others, that economic freedom with certain socialist characteristics can create conditions for economic growth than can keep the population happy and at least passive enough with 'what they got' to keep from overthrowing the regime. But, as noted by the Chinese Communist Party themselves, if the state isn't able to keep up economic growth and low unemployment isn't sustained, the people are going to have something to fight against. And, as we know, capitalism does happen to follow patterns and cycles of boom and bust, no matter how managed it is.
Furthermore, the precedent of the PRC to keep stability the way they have might be fundamentally Chinese. Their Communists were only established after World War II, and were credited with success in wartime conditions to establish peace and modernizing services to the people. While the Chinese can point to the Great Leap Forward, Cultural Revolution, and other Maoist policies that were blatantly destructive to the Chinese people, the Russians at 1990 could point to Brezhnev era stagnation, to a long series of purges and political repression, to gulags littered throughout Siberia and Russian history, to collectivization, to horrors and atrocities not just attributed to one personality, as in China (Mao Zedong), but to Lenin, Stalin, Brezhnev and others (Beria, Sverdlov, etc). Those responsible for the horrors of Russian Communism was the Communist Party, not just one deviant (as Mao in China). So, one can not equate something that worked in China with what might have worked in Russia. There are a lot of other factors: cultural, ethnic, demographic, economic that also fall into place differentiating Russian and Chinese Communists.
Back to the initial prompt: how could the USSR survive to 2008? Here's the tough part, despite the initial PODs: we live in a world where computers, instantaneous communication, and the internet are consuming more and more of our lives. In fact, the 2000s might be known as the decade when it became a global phenomenon. As glasnost proved: the Russian people, with the conditions they had lived through during their generation, could not stay loyal to the state when they were able to voice their opinions. The freedom of speech was wonderful and incited people to attach a lot of passion to it, and it turned out to be directed against the oppressive regime they lived in. Getting rid of glasnost and perestroika is a vital first step to continue the Soviet Union, but the invasion of the Internet into Russia could accomplish what glasnost accomplished in the 80s and 90s.
The Soviet Union would definitely benefit from new information systems. Computers could work wonders in the management of the huge and complex economy of the post-industrial world. With the capacity to store information and calculate mathematically certain necessities, the computer would literally revolutionize the Kremlin and the way the Soviet Union is run. It could help hone economic controls to perfection, so that instead of the free market keeping products balanced correctly with prices, the state could actually figure out the same. Perhaps this kind of digitalized central economic planning could even be better than the free market of today, if I might be so bold.
The problem is that the use of the computer brings the use of the Internet, eventually, which the Soviet Union might believe to be a great tool for the collectivization of culture and society within the USSR. In fact, the Internet really does fit the requirements of a 'socialist wonder machine' that the Soviet Union would have loved. In reality, the Internet would have brought the Soviet Union down even faster: like glasnost only multiple times more effective.
I guess I shouldn't say the Soviets would adopt the internet immediately. They'd realize the potential problems with the Internet, I would think, if Gorbachev or another reformer was at the head of the Union. The Internet is still necessary, due to its advantages in nuclear war scenarios, but in the USSR it would be limited to the USSR and under heavy state and military control. Perhaps universities as well, maybe even for certain professions but it would be monitored.
Now that we're passed the Internet/Computers discussion, what you need is Kruschev to stay in power the longest he can, and to be followed by someone who is between Brezhnev and Gorbachev in political affiliation. There needs to be room for economic growth, diversification, adaption to world markets, etc. etc. but the leader can't be so much a utopian reformer that he gets rid of the political and economic controls that make the USSR possible.
There's some more specific things that could have been done for a USSR in 2008, I'll come back to this thread later.