We had a hard time finding any insulation to fit between our 26"-on-center joists in a back room ceiling. So, we bought 23" wide stone wool batts. We're trying to determine what is the best way to hold the narrower-than-the-space batts. Right now we're looking at cutting and installing multiple short pieces behind the vapor barrier rather than two long ones. The metal pins that we bought aren't long enough. Is there another way to secure the batts in the wide space?