Mec-gear makes flush fitting 18rd mags for the 226, so a 20rd that protrudes slightly from the grip doesn't seem out of the realm of possibility.
Mec-gear makes increased capacity flush fitting mags for a bunch of guns, and unlike some aftermarket mag companies (i.e. pro-mag), their mags are good. For example, they sell mags for the regular XD's that bring their capacity up to that of the XDM models.