Add a contribution and associate it with an existing event

Currently It is not possible to add a contribution to a persons record and associate it with an existing event the user registered for. (See attached fictional screenshot including fictional helptext)

This functionallity is very usefull in case you want to correct or change contributions after registration. It would be possible to add and associate discounts as well as aditional costs / contributions for workshops / lunches / etcetera. These changes / corrections often come in by phone or email after registration.
Currently the contributions that are used to handle it do not show up in the financial event repports.

Adding this will help us very practically in the administration of summercamp registration but I believe it is a real life scenario for a lot of organisations.

BTW. Associating a contribution is one way to approach the lacking functionality. Another would be from within the event registered for, to allow editing/changing the existing price-set. This would be the neatest solution actually.