Yes, you can use a micro that is wider than the range. LG makes a 24" one, though.

If you can fit a 30" opening you will have a lot more choices. Only one 24" (the LG) that I know of.

Thanks Texas and Writer. I saw the LG but the reviews were horribe. So I guess I'll go with a 30" which does have lots of choices, even though the alignment will look dorky!

>the alignment will look dorky!

Not necessarily, although it may be tricky to get it properly on center with the stove. A neighbor of mine had a similar situation (she knew she wanted a 30 because she wanted convection, but only a 27" cooktop), and she was able to make it work by swapping the cabinets on either side of the cooktop, so below she had 18" base, 24" cooktop cabinet, rest of run, while above she had a fifteen inch cab, the micro 30" cab, and then the rest of the run. It's only three inches each side, after all. Many times a hood is at least that much wider than the range it's over.