You can get moderator adaptors for quite a few of the CO2 pistols, and they are effective. Obviously the width of a good silencer does often force you to use a red dot or scope rather than the irons.
I have moddy adaptors for my Umarex 1911 and S+W 586. The 1911 gets away with it because it has tall target sights, but I needed to mount a red dot to the 586.