im currently pondering this issue as well, but theoretically, it IS possible, not too sure how practical isit to do. check out this page
http://scoobysworkshop.com/gainingMuscle.htm

but i guess its easier to bulk up and gain some fat during the process, then lose it afterward. not sure if its true, but with the extra fat u gain, it increases your testosterone production which in turn helps in bulking of muscle? any comments from the pros?