Gift Aid boolean

Hi! This is a feature / quick hack request...

In the UK, we have something called "Gift Aid", where any taxpayer donating to a charity can make a declaration that will allow the charity to claim tax back on the donation.

I need to allow the user the option, when making a donation, to check a "This donation is Gift Aid" boolean and record this alongside the donation.

I'm assuming this functionality isn't currently in the plugin. What do you recommend as the best way to achieve this just now?

Thanks