Hi
Actually, you should separate the operations that absolutely must be done on the EDT with a current OpenGL context from the others. Moreover, you don't need to make the OpenGL context current on the EDT when you use your offscreen drawable, you can choose another thread. You can use a Swing Worker and call setProgress or something similar from another thread (not the EDT).
Finally, you can split your whole job into smaller tasks and execute each task one by one. This is what I do in my game and in my editor. It allows me to block my (non AWT) progress bar only during the execution of each task and I can update it before starting the execution of another task.
Good luck.