Need to exclude all 3rd party Vendors from coupons without sacrificing excluded products

At the moment we are developing the ability for 3rd party Vendors to use our checkout and hawk their products. As a part of that we need to prevent our current coupons from applying to these 3rd party vendors.  We have so far attempted to preserve other product exclusions/inclusions using parent coupons.

It works somewhat as is, but if one of the products is attached to our vendor and in the same cart as a third party product, the percentage based coupons applies to the whole order. Is there anything that we can do to make sure the coupon applying the vendor exclusion effects the order properly in this case?

The parent coupon used currently has a coupon with a discount of zero that contains the vendor inclusion rule, for further information.

As a part of that we need to prevent our current coupons from applying to these 3rd party vendors.

This does work to a  degree. However we've run into an issue where when one of the first party products and the the third party products are in the same cart, if the discounted amount is a percentage it will still be applied to the order because that first party product is in the cart.

Is there anything that can be done out of the box to make sure that these discount percentage coupons, when part of a parent coupon only apply to our first party vendor products.