Hi Finnur, thanks for the offer to contribute. If you want to make code enhancements to the Image Gallery module, the source code is all available to you. To me your proposed changes sound like a good enhancement for mojoPortal, but you should probably wait for Joe Audette to weigh in here, to make sure that he is interested in including this enhanced functionality within the mojoPortal core. If he is, you'll need to send him a signed contributor agreement, and then you can work to improve the Image Gallery module to meet your needs, and if Joe approves your changes, he'll incorporate them into the core.
If Joe does not want your changes to be part of mojoPortal itself, you can always clone the Image Gallery feature and make changes to that for your own use. That way you will avoid forking the code and can continue to upgrade in the future.
It does sound like IndigoTea may have a very nice solution as well, if you're interested in going the add-on feature route.
Jamie