Grant Payment from Endowment Fund to pay on Pledge

We have a client who gave us a pledge of $50k. He has given us $20k towards pledge. Because of better tax benefits, he wants to transfer $10k of his outstanding balance to a community foundation which has an endowment with us. This endowment's funds are untouchable- except for the investment monies earned. I am trying to think of a way to “keep” the pledge the same amount so it doesn't interfere with total raised and to make sure he “gets credit” for entire amount, but I'm at a loss as to how to do that since we won't “realize” that $10k in one year. It could be several years. I don't want to leave a pledge “open” for 10 years and I truly have no clue how I can document this in RE.

Any help would be appreciated.

Thanks

Tiki