With all the talk about "does the software support fractional bpm" wouldn't you just create it at say 124bpm and then scale down to 123.45 (or whatever) by taking the total length and scaling it by that percentage (e.g. 0.99561926612903225806451612903226). You don't even need to scale it trying to keep the pitch correct. You just speed it up < half a percent, the pitch rises slightly, and you have your perfect bpm.