How feasible is this?

I create sites that raise money for charities thru’ affiliate sales. I’d like it use wordpress as it is so easy to set up and maintain.

What I need is the facility for a visitor/user to register and choose the charity they’d like to support. Then when they click an ad or visit a store it passes that info (with a simple ref value) so I can track where the donations should go.

Is this relatively straightforward or should I be looking for a genuinely custom website?

Thanks for any ideas or advice,
Nick