There's no way early on for the Soviets to catch up without wrecking their economy? Okay, not exact perhaps, but close enough that the USA can't throw its weight around as much.
I think the only way to do that is not to improve the Soviets' efforts, but to retard the American program. The Soviets were basically going flat-out on the bomb, I don't think they could go any faster than they were, but that doesn't change the fact the US had a four year head start.
There might be some way to delay the US bomb program. Things were kind of a mess between 1945 and 1948. The Army was running things from 45 to 47 but everyone knew that control was going to be handed over to a civilian agency, so the Army didn't feel it could commit to any long-term projects. From 47 to 48, the new commission was running around trying to do everything at once without the manpower and administrative structure that they needed.
Morale was in the crapper at most of the labs. Personnel, especially scientists, were leaving for the civilian sector. There was some labor unrest, including at least one threatened strike. There were tens of thousands of people who'd been hired without proper background checks during the war and had to be rechecked. And there was a certain naivete in the officialdom, at least outside the AEC itself, believing our atomic shield was stronger than it actually was.
A lot of this was just the inevitable problems of any new agency, but there might be a way to really gum up the works long enough for the Soviets to catch up by the early 50s. But it would not be easy. A good start would be reducing international tensions so that the AEC is a lower budgeting priority, but that's only a start. Another thing would be keeping the McMahon Bill from passing in the 1947 legislative season - there was quite a fight over it in congress, particularly over the question of civilian versus military control. Another year without the bill means another year of the Army holding down the fort without a mandate to do anything long-term.
Honestly, though, I don't know if it could be done. The bomb was the US' big advantage, our ace, and we were going to exploit it as best we could.