Interesting, my theory about this is that since you are sitting down and doing pretty much nothing, it calms you down and as you calm down, your dream stabilizes. So then in theory, just about anything that is boring or will calm you down in your dream should make the dream stabilize and last much longer than normal.

If this is the case, then I recommend that you can like Skully suggested, use a blank white space and stay there or just stay in a regular environment but instead of being excited and flying, just simply walk around for a few minutes, or if you wish to go to the extreme for a few days. It should stabilize the dream.