My mom taught me a trick that I used for my current project. If you need to glue a hollow object to a flush surface, a hot glue gun will make things easier. This trick gives your hollow object a flat surface to glue securely to another object.
Simply fill the hollow object (mine is a dresser handle) with hot glue.
When you get to the top, use a putty knife to scrape off any bumps the glue leaves. This will help give you a flat surface to work with. You have to scrape quickly as the glue sets up almost immediately. The glue left on your putty knife will come off easily. Now your hollow object is ready for gluing.