Paying a share of selected sales to a customer by Gemma de Wind

I'm an artist setting up an online gallery with Shopify. I'm going to offer limited editions prints of existing artworks as well as commissions packages where people can have an artwork created of their own car (My first collection features cars but the same principle will probably apply for everything I do). I've developed a business model in which commissions customers can let me sell prints of the artwork I create for them in exchange for a 5% share of the sale. (Forgive the wordiness, I'm trying not to confuse the point by mixing up "sales commission" with "art commission").

Ideally I'd like to find an app that lets me select which individual artworks are aligned with a specific customer, calculate their sales share on prints at the point of sale and have it allocated to a separate account for them. They can log in at their leisure, see how much their car has earned them and either wait for it to build up or request to have it paid out through paypal. A bit like an affiliate program, minus the referral part.
Does anyone know of a shopify app that could manage this for me?

Thanks in advance :)