Seems pilot mates are being brought into the reasoning now.
If you are both flying them get him to contribute - as a mate and myself do, we both fly half way and we split the costs therefore we are still paying 100% of our costs for loggable hours.
If I was invited by a pilot and was asked for half the costs I would say "Sure, I take it I am logging half the P1 hours then?"
You cant have it both ways.