I've discovered a nice solution to this problem.
Quine-McCluskey is able to handle a truth-table where some of the terms are marked as "don't care", which means that the term will never occur, so the minimized expression can return true or false.
A B result
0 0 0
0 1 don't care
1 0 don't care
1 1 con't care
It can clearly be seen that the above function can be minimized to just return 'false', as that is the only result that we care about.
So to deal with known terms, all that has to be done is set the result to "don't care" for any terms in the truth table where a known term evaluates to false. The Quine-McCluskey algorithm then generates the minimized function taking the known terms into account.
For example, if we have a function of A and B, and we know that
A == false, then any line on the truth-table where A is true can be marked as "don't care" because we know it will never occur.