Gommie does boring for a mini freak insert (cut down standard inserts), the reason its not widely offered is its not as straight forward as people think, its a long way down using a small diameter boring bar, and you get quite bad push off further down you go into the barrel, on a cnc lathe you can adjust the taper but then its just not cost effective.
Also even the people that do offer the service ive not seen 1 that's been done correctly even the mini inserts, the reason I say this as genuine freak backs have 2 internal orings which stop the insert from moving around once in place, if you don't have these there is nothing stopping the insert from twisting or vibrating