No reason that you couldn't....the saw needs to be at a 45deg angle, and the rail would need to be at a 45deg angle, the same way you would cut crown on a tablesaw, except that that on the tablesaw, you would use a miter guage. It would, however, take a lot of trial and error to get it dead on...and cutting crown is always a mind-bender (at least for me..)
However...personally, I wouldn't do it. I think that it's much easier to cut crown on a miter saw with crown stops. This way, you set the crown stops to be perfect, and then you only have to rely on the 45deg stop on the miter saw to be dead on.
That being said, crown miters (compound miters) is the only time that I use the miter saw for miters....all other times it's either the tablesaw or MFT...much more accurate.