I went to the hardware store today (it's right across the street from us) and was given a suggestion of a heavy duty packing tape. I bought it and tested it and it seems to work on the styrofoam. Now the problem is that I won't have the time or space to do the blocking of the shawl until sometime next week. :(
I did, however, get all the pieces cut for the class sample that I'm making. Let's hope nothing happens on the way to Sunday to keep me from getting it done! I only want to finish the top, not the quilting, so the students can see it with the paper on the back.