Boris Nemtsov(governor of Novgorod) and Grigori Yavlinsky (deputy chairman and author of 500 days reform) had some political basis in the USSR, so they might work if you want a liberal government, though they're unlikely to be elected. Yegor Gaidar was prime minister by late 1991, so depending on what happens to Yeltsin he might have a shot at being the chief of the liberal camp. The liberals would likely be in opposition since the vice president in 1991 was A. Rutskoy, a man who is generally not viewed as very liberal at all (nor was the RSFR soviet). All of these candidates are possible in the same time frame: the Russian liberal opposition was and is famously purist and tended to fracture. Shevardnadze has little chance of being president of the RSFR (which was Yeltsin's post) since his authority was purely in the central soviet government (which was dissolved in 1991).