1) glCopyTexImage2D - www.opengl.org/sdk/docs/man/xhtml/glCopyTexImage2D.xml
2) dome post_draw. Now dome mode can also use scene.post_draw. It only runs for the last scene. It's really useful. I'm working on a nice showcase for this (a dome visualizer for the dome mode running with bgl. In the mean time this is a (lame) example of both working together (the buffer is being copied and draw on top of the window):
http://blenderecia.orgfree.com/blender/tmp/dome_bgl_copytex2d.jpg
