Sadly your options are limited to; either getting a narrower bore silencer, or holding out hope for a set of adjustable competition sights to come up for sale 2nd hand. One has come and gone in the last week on here.
The rear adjustable comp sights will fit the Umarex 1911, CP88 and Beretta (don't know about the CP99), but the foresights are unique to each gun I believe. The rear sights are rare, and the foresights sadly even rarer.
A real shame, as silencer issues aside the adjustable sights make them much better guns IMO.