Don't apply discount when another discount is already applied

[bartrylant]

What are you trying to do?
I have a site where member from a certain user group (diamond members) get 10% discount on everything. However, sometimes I also do a "20% discount on items in this category if you buy 2". For the diamond members, I want them to get the 20% discount on the eligible items, and still get 10% on the other items. Therefore I cannot say Don’t apply any subsequent discounts to an order if this discount is applied (otherwise it would just stop after giving the 20% for multibuy, and not the 10% for the diamond members).

What's your proposed solution?
Just like we have an Exclude this discount for products that are already on sale option, it would be nice to have an Exclude this discount for products that already have a discount applied option.