The option to put a voluntary donation onto a DIY form would be very useful, as you cannot edit the payment sections on event registration forms. In our charity, we are currently recruiting runners for an event, and we want to get as many people as possible. In order to not put some people off from entering, we have asked that if they do not wish to raise sponsorship, they can make a donation instead. The only solution to this at the moment is to put a link to another donation form, which means that it is yet another form for the runners to fill in. It may also be useful to add to a newsletter sign up page.