I have run into similar situations, not only in my pack but other organizations. I always start by thanking them for their generosity, and explain that if the money isn't used, it may not be budgeted in future years. Where it hurts the pack is that a future leader may not have the same resources to make a similar donation and will be intimated from asking for reimbursement, or worse yet, not lead all together. It allows for better tracking of the expenses.
No easy answer, but I hope it offers a helpful idea!
