This seems more like eating broccoli than keeping up motivation. If that's the case then it's better to force feed yourself. Clear your schedule, pick a day, go into your /etc/hosts and block every other site that you don't need in order to finish your rewrite, drink a cup of coffee and then don't leave your seat except to go to the bathroom. If the work spills into the next day then so be it but get it done in one session. There is no easy way around working with code you hate. Some people say use moderation and do it slowly but dealing with badly cooked broccoli sucks. Shove it down your throat and finish with a chaser.

If you want it badly enough then just force it. The rewrite should only happen once.