Question about Parallel Payments and Global Carts

Hello. I have been looking at a way to have a global cart and also take a % of every transaction. I know currently this is not possible with MarketPress but I have two proposed solutions and I wonder if anyone would know how I would go about implementing them.

1) From what I understand, Parallel payments work with a global cart, where it divides up the money and sends it to the appropriate seller. With this in mind. Couldn’t an extra fake item be added to the order with myself as the receiver. The amount could simple be a percentage of the entire transaction.

Example:

Buyers order: (3 items)

$10 shoes from Store #1

$5 shirt from Store #2

$1.50 fee to the network owner.

It’s simply as if he is buying three items, where as the third item is calculated based off his order total.

Proposed solution #2:

PayPal chained payments is used where me (the network owner) is set as the primary seller and all the other stores are set as secondary sellers. I understand it would show the transaction is going to me and not the individual store owner, but this works perfectly with how I have my store set up anyway.