Payment validation errors when billing fields are customized

We have a deployment of CiviCRM with an extension that hides some of the billing credit card fields, and makes them not mandatory. This used to work fine in 4.6.

When migrating to 4.7, credit card contributions stopped working. Any attempt failed with a validation error because of missing billing fields.

From what I can see in the code, this happens because the piece of code that makes this validation was moved, and now uses a hard-coded list of fields instead of reading them from the form. The class that does this validation does not have access to the form, so the way I fixed it in our deployment was to move the validation back to its original place:
https://github.com/WeMoveEU/wemove-civicrm/commit/f784162df3f5b42f020472fd470373ba1f9dac8a

I'm pretty sure this is not generic enough to submit as a patch, but if it is, or if I can be provided guidance to make it more generic, I'll be happy to submit a PR.