I would love to be able to do this. As the feature is implemented now, it seems the Custom Form option appended to a product is missing a couple of features I want in a form. The primary one is the ability to share the data with another service or automatically export it.
Ideally, I'd like to populate a Google form with entries. I can do that with a regular form, but then it's not tied to the purchase. How difficult or simple is that script to write?