You could always put a black turtle neck sweater on and have it rolled up. shoot against black.
What everyone else has offered. It is perfect advice. Try not during the session to make a big deal about it, in fact make changes in angle during general conversation. It is kind of funny that: we are all the same! but this uniqueness of appearance that seperates us as individuals we try to correct uniformly. But every person needs this and it is different with everyone. So the challenge here is to solve the problem without warning so that their stress about it does not show up in the images. It is very easy once you have the awareness to see it, to solve. So don't stress, have fun and solve gently.