The interesting thing is that when using Sputnik's Flyback F1 to launch the stock Atlantis, I manage to fly both vehicles at the same time fairly easily. After seperation, I fly the shuttle until the F1 is about to reenter, then I place the shuttle in a good attitude and fly the F1 until I have it in a straight and level flight back to the Cape, at which time I finish flying the shuttle to MECO. Then I switch back to the F1 and land it, being careful not to forget about the OMS2 burn! Quite a workload, and 2 boosters would be too much, but one is just about managable enough.