It's always a bit diffcult to reccomend something for a situation like
this when you cant see it. One thing for certin, glue isn't the
answer. No matter how good the glue is it is only as strong as what
you are gluing it too. In the case of dry wall, you are gluing to
paper or plaster. No holding strength there. The previous post
mentioned molly bolts. That's what is usually used to mount something
like this unless you are lucky enough to have your attachment point
fall on a stud.