How do you distribute secret shares without knowing who to first distribute them to?
As long as you know the reconstruction threshold a priori, I see no reason you can't generate a bunch of shares before knowing who you will distribute them to. Once you know who you are going to distribute them to, just send one share to each person.

On the other hand, if you don't know the reconstruction threshold, you wouldn't be able to construct, I don't see how you can do it. It would seem like an ill-posed problem at that point.