I've tried using mantras in this manner before with a bit of success and have been recently been thinking about trying it again, just to prove to myself that I have free will during my non-lucid dreams.

One time, I tried this by repeating I'm dreaming over and over while falling asleep in an attempt to say I'm dreaming during the dream. I actually did successfully incubate saying "I'm dreaming" during the dream, but a DC replied "No you aren't," and I said "Okay!" and never became lucid.

I think this has potential, but the main problem I've found with it is that many times it takes me a lot of time to fall asleep while repeating a mantra, and frankly I find it a bit of a pain repeating a mantra. I think these problems are fixable though, so I'm trying to figure how to fall asleep faster while repeating a mantra. I think that will be my project tonight.