I'm using CiviCRM's "pay later" functionality on a contribution page and have received a number of contributions that now have a "pending" status. This is good. When I receive a paper check, I can just update that contribution.
However, some donors wish to fulfill their pay-later pledge online instead of by check. Is there a way for the donor to pay online such that the "pending" contribution will be automatically removed or updated?
Note: I am using a thermometer to display the total amount raised and it includes pay-later contributions, which is important to me. I'd like to avoid having duplicate contributions in the thermometer.