Add product(s) on the fly to existing order

[iroller]

What im looking for is a way to add a product not in my database to an existing order in oscom. I have thousands of old car parts im constantly putting up on my store, but when someone needs a non-stock part(usually a used part i have to go and pull off a car i have), i have no way to add it to an existing order. Would this be possible? Can 'Manual Order Maker' do this? Thanks in advance!