I think its ok to freeze pyrex. the potential problem with freezing stuff in glass containers is that stuff with a lot of water content expands when frozen, but the pyrex won't so it might crack. i think i would try it but dont fill the container too much? what do others think?
I line mine with saran wrap and when it's frozen solid I pop out the frozen block & peel off the saran wrap. That way I can use the pan while keeping the other item frozen. Of course, I put the frozen thing in a plastic bag, so I guess that won't help you not use plastic! Either way, the pan in fine to freeze in.