Embed 'donation' with event price?

[zorgalina]

What about adding a 'donation' price field (set) that could be added to an 'event' price set? If a person is buying a ticket to an event, they may 'donate' some amount (e.g. USD 5.00) in the same transaction, but would get a 'thank you' for donating, as a receipt, and the amount would go into 'contributions'?  This could be nice for non-profits where you need small donations but don't want to make users use a whole other form to make a donation, if they're already paying a fee for an event.