which mouse are you using?
EDIT--
Look into Autohotkey. It's a standalone app (that's kosher with blizzard as long as you maintain the 1-keystroke-1-action rule) that's used by a lot of multiboxers.
It'll take a little bit of learning and sleuthing to figure out, but it'll let you remap say home to shift with something like
Code:
#ifWinActive World of Warcraft
!HOME::
Send !{SHIFT}
return
That's dug up and modified, and largely untested. you'll want to look up some docs if it dosen't work. you should be able to sub out HOME and SHIFT for whatever.