Possibly using hairspray. I just did a show with a faux fur rug that someone rolled around on, and even after combing and trying to get the loose fur out, it still shed a lot.
We used aerosol. I don't think the other type of hairspray would work well. And I would do a heavy coat after the performance, after the actors have left (you know how actors can get with hairspray when they aren't the ones applying it.), and I would do a small coat during preshow. No one complained, and it worked fairly well.
I don't know how much that would translate to feather boas, but it could be worth a try.