Plugin for donating a percentage of sales to a charity

Hello all,

I am searching for a solution to the following scenario –

We have an online shop http://www.earshop.com running with Jigoshop and Fresh Shop as the theme.

We would like to donate a percentage of the sales to a charity if the buyer was referred by this charity.

Is there a plugin that would be able to do this? Or is there a better way to achieve this? It is the intention that the same scenario be applied to other charities in the future, and all these would run alongside each other with donations going to whichever charity the buyer was referred through.

Or perhaps it would be better to simply have bulleted points on the checkout page that asks which charity referred them?

Our intention is to pay the charity in bulk periodically rather than have their percentage automatically go to them on each sale.

Any ideas or pointers on this would be greatly appreciated.