This morning I took in a talk on communicating with donors. At one point in the talk, the speaker made the following comment: "If you don't have a relationship with a donor, you shouldn't accept their gift". Think about that for a second. Money without relationship isn't worth the money.
Part of the reason for that is the fact that a donor who is giving you a gift (of any denomination) is expressing an interest in you. In giving you money, they are at the same time saying that they care to be involved in your work. As such, to take that person's money outside of a relationship with them would actually be doing the donor a disservice.
Honour their gift. Find out why they cared enough to give. You might just find that you don't just have a donor, you have an advocate, a volunteer or a brand story to tell.