Coming for GP 2013 Microsoft has a new Feature of the Day: Manual Prepayments
Feature of the Day: Manual Prepayments – Inside Microsoft Dynamics GP – Site Home – MSDN Blogs
Tips & Hidden FeaturesMicrosoft & the GP EcosystemGP 2013
Archived post from 2012. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.