A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 102,617
If I understand correctly, the suggestion is to get DL to donate some miles to the charity, whereas the OP wants to donate his own miles.
The OP could add something to the package, perhaps car service to/from the airport for the trip. It might be easier to keep the donation in terms with a clear monetary value for tax purposes rather than miles and points.