What I would like to see, is a possibility of joining them demonic forces, at least at some point, even if that would be a one-time chance.

Not every sod who winded up in some bizzare version of hell shall be bent on escaping the realm. Or maybe later they realized the hopelessness of the case, and opted for this (recently made available?) fraternization option.

Nevertheless, the offer ought to be sweet; no man ever wetted the clay expecting the bricks to happen themselves, so provide good stuff (powers, servants, positions, stuff like that) in the exchange. You can always make it a deal with a catch, hehe...