Easy way to split up payments for cart items based on a Member ID?

I've got eCart setup and I included a custom column called MemberID. I need to create a checkout system that splits up the payments so each seller receives their money directly.

For example, say there are 5 items on the cart. 2 belong to seller 1 and totals $20.00, 2 belong to seller 2 and totals $10.00, and 1 belongs to seller 3 and totals $25.00. I need to somehow make this available to my application so I can generate my own calls to authorize.net...one for each payment on the split order.

So a single order that the buyer sees a grand total of $55.00 needs to split into 3 differnet payments to 3 different sellers: 20.00, 25.00, and 10.00.

The MemberID in the shopping cart should make this easy on me but I'm just not seeing the best way to do this. I can handle the calls to Authorize.net once I have my 3 seprate totals pulled out, I just need those 3 seprate totals (or however many different sellers are on any given order.)

Any information on how I can handle this would be greatly appreciated. thanks!