Turning down a scholarship...with the hope of getting more funding?
"I appreciate this opportunity and would love to attend, but, unfortunately, cannot afford the tuition" - that's pretty much the situation according to your description. It's not flattery, it's not manipulation, it's the fact, isn't it? It sounds just right. 

It gives the commission full discretion to decide whether they consider you worth being helped over this hurdle. 

Just don't decide to join, after all, at this support level without having a very good idea how to justify where your suddenly newfound riches have come from.