My dad used to be like this. We'd go out and buy him pressies anyway and although he was grateful he'd still say, "you shouldn't have wasted your money - bar of chocolate would be enough."
Only thing is, Dad wasn't much of a one for charity (although he was generous to a fault with the family), so he'd still have said we were wasting our money. However, if you know your dad has his favourite causes and/or charities, then I think what you propose would be an excellent idea. If it was doing someone else some good, he couldn't complain really, could he.
What about sponsoring a child on his behalf through World Vision? Or what you could do is to first help a homeless person by buying a copy of The Big Issue, and then have a look at all the charity appeals/ads in its pages.