I added a little section onto the feat I made.
Now, in the same way that clerics with at least 5 ranks in Knowledge (Religion) get a +2 bonus on turn checks, so to does the DC of Blasphemous Secrets increase by +2 if you have at least 5 ranks in Knowledge (forbidden lore).

It will make yourself more vulnerable to blasphemous secrets, true, but you were already going insane anyway.