Thanks, I actually e-mailed Green Glue Co. right after I posted this message. I'll see what they say.
As for opening up the wall, that's just not an option. I live in a Manhattan co-op. Who knows how they'd feel about that. However, I suppose it is possible for me to attach a layer of drywall to my plaster and then green glue, and then drywall again. Not something I'd ideally like to do. Or perhaps better still, I can apply green glue to plaster wall, then dry wall, then green glue again, then drywall. Certainly ups the cost a bit, but perhaps that's a consideration.
Oh, and the wall I'm looking to do is about 140 sq ft. One case is preetty much exactly what I need for one layer (if I use it all , it would come to somwhere between 2 and 3 tubes per sheetrock, so that works out)> needless to say, this is all very stressful!