A passenger (or passengers) can contribute to the cost of a plane (in the UK) provided the Private pilot pays the greater percentage (I forget how great - but will look it up again)
I wonder if a sponsor could be treated like a part paying passneger who never gets on the plane......It's a grey area and I guess one only the Caa can answer. The easy answer from them would be NO, but I'm hoping for a reasonable amount of consideration before they reach a decision.