MarketPress coupon plugin engine

I have a client who wants all the custom coupon options I've seen listed in the forum plus a few.
I'm going to code them and I'm considering making them available, but it looks like I'll end up with a fork of MP if I have to rewrite how coupons are handled.

I saw one of the staff here suggest using a shipping plugin, but since we can only use a single shipping plugin at a time, that means I'd have to add the coupon features to each of the shipping plugins out there (which I just did for "Free Shipping Over $X" and it wasn't the ideal way to do it).

What I'd like, is someone familiar with the internals, like Aaron (or whomever), to replicate the way payment and shipping plugins are hooked and used for the coupon functions. If it would allow multiple coupon plugin types to be active and then each new coupon code would be defined by one of the plugins like the current shipping/payment plugins do.

Then we can crank out those new coupon methods and everyone's happy!
Otherwise, I have to patch MP with every new release and nobody's happy.

I'm really not keen on tearing into the internals of MP myself, but I'll do that if needed.
Thanks.