Then don't consider it a donation, but as a separate pricing tier. Currently, you are charging $5000 to those who don't want AGPL, and $0 to those who are fine

Then don't consider it a donation, but as a separate pricing tier. Currently, you are charging $5000 to those who don't want AGPL, and $0 to those who are fine with AGPL. You can charge, say, $100 to those who are fine with AGPL but want to pay. If you want to increase sale, you could include donors' names in the documentation in return to $100, for example.