I'm going to throw out a theory here not sure if it has already been mentioned or not. Why not simply create many memories in your lucid dream and let your mind fill in the details when you wake up. I've personally had dreams that have lasted days in dreamtime, but don't seem that long. If my conscious awake brain comes up with things to fill the gaps which it has before, then dreams that feel like 30 minutes seem like they lasted longer after I woke up.

This isn't really time dilation for say, but rather is like tricking your mind into thinking you had longer dreams. Sadly this doesn't help if you want a really long lucid dream, but can be very useful for non-lucid dreams.