Evaluate prices for specific customer or visitor groups

I have a need to provide specific customer or visitor groups to the promotion engine when calling Evaluate or GetDiscountedPrices.

The use case is pretty straight forward: a client wants to display two different price on their variant page:

1. The actual price the customer has to pay for the variant.
2. The member price that the customer would get if they were a member (hidden if they already are a member).

It must be supported that the displayed member price is applied through promotions as well as a direct price on the variant.