Add an option to limit the 'buy x, get y' usage per order.

I have following issue:

Our customer wants to give a promotion when buying:
- 2 times product A: 10 euro
- Product A and B: 10 euro
- Product A and C: 10 euro

So I configured: buy X, get Y and added 10 euro as a discount.

When a customer buys 5 times product A, the discount of 10 euro gets applied 2 times by design.
I want to limit the usage of this promotion per order, so the customer only gets 1 time 10 euro discount.

I'll be looking into implementing this in a custom condition for now (I guess) and I will keep you guys posted on progress.
Maybe it can be interesting to implement this too?