I don't think this is true. Suppose world A is rich and world B is poor. People want resources more in world B, so they are not willing to pay as many resources for a certificate. But on the flip side, a philanthropist is happy to accept fewer resources. That is, a resource that pays $1 (real) in world B, costs more than a resource that pays $1 (real) in world A, because it's catastrophe insurance. This seems to exactly offset the decreased willingness to pay of people in world B.

(Of course, wealthier worlds might also devote a larger share of their resources to philanthropy, and so for that reason might be better to support, though by a much smaller factor. This proposal allows such worlds to reap benefits from their increased philanthropic spending, while poorer worlds can't do so. We could prevent this inequality by leveling down, but I don't see why we should.)