Maybe you've heard of affirmations. Things you tell yourself over and over again. usually to give yourself a boost.

Try on the last few miles of your ride reminding yourself how much fun you just had, or how you reached that goal you set for yourself, or how you just did this ride ten minutes faster than usual, or how you are already looking forward to the next ride. Leave yourself with a good feeling about it, and you'll be anxious to come back to it.