The more for the airlines to foot the bill. If the customation is intended for their use, the airline should pay for it.
If the key issue here is to get a type rating it should be only a type rating, just learning to fly the aircraft, nothing more. If you start adding company specific procedures, that should be the responsability of the airline not the pilot.
You as a selfsponsored pilot are paying for the type and for the company specific bits. That's unfair!
But then again who ever said life was fair.....
