It's not a terrible idea. From having played enough Kerbal Space Program to get a rudimentary but experience-based understanding of orbital mechanics, I know that the biggest chunk of delta-v for an orbit is horizontal velocity, not altitude. Obviously, balloons won't provide that. However, shoving a launch stack through the thick air near the surface is also quite a bit of work--go too fast, and you waste fuel fighting drag. Go too slow, and you waste fuel counteracting gravity*. I've thought about using air-breathing first stages to deal with this, but the balloons just might do the trick.
* For example, consider the worst-case scenario in which the rocket puts out exactly 1 g of thrust and merely hovers over the pad, not gaining any speed or altitude--ALL the fuel burned like that is wasted.
Like some sort of . . . rocket raccoon?