In reply to cmb621: I have two sizes difference between my feet but have always worn the same size shoes, I fit them tight to the big foot which does leace the other a little floppy so not so great on the tip of the toe, but fine for edging. Laces all the way down help a lot and I always wear socks even when I fit them without socks, helps to make the tight shoe a touch more comfy and packs out the gaps in the other one.
Other than that you just get used to climbing slightly differently with each foot. The loose shoe is much less painfull to foot jam with for instance!