E.g. I want to donate to Shrimp Welfare Project (SWP), which is not tax-deductible in my country, but the Against Malaria Foundation (AMF) is. So I team up with an American who wanted to donate to AMF, and now they donate to SWP and I donate to AMF, so now both our donations are tax-deductible.
Great question, maybe someone should set up some kind of moral trade ‘exchange’ platform.
Quick related PSA in case it's not obvious: typically donation swapping for political campaigns (i.e. with individual contribution caps) is extremely illegal…