This one helps me alot, its best done daily. I pull it out when I get stumped on something.
Take a piece of paper, pen. Sit and write with no distractions for a minimum of 20 minutes. Better if its 30. DO it twice a day if you can find the time. So, you ask, what the hell do I write about? Anything you want, with no holds barred. Let it fly. The point it to WRITE, not the outcome. Just write, your hands are cramping up, you need to gas up, don't have time to do this etc. If I were to do it, this is how maybe I would start...
"I hate having to cook up some great words, only to end up with something so mediocre that a 4 year old could write better than what I'm producing. I'm listening to Politics of ecstasy. I wish I could just whip out great phrases and their perfect placement, all standing in line according to power, height, weight. I fucking hate drawing a blank. Hate it. Hate it. This excercise sucks. Sucks! And it also works, so I stick to it....I can't find my words, they're waiting to come out, the most powerful first, the heaviest last, the pairing of words so enormous they'll never be forgotten. <------ AHAHAHAHAH! LMAO. I made a funny. As I write, I always wish for that to happen. The not achieving it, or coming close to it is what holds me back so much. One day if I did achieve this "perfect pairing of words" ... what would happen? Would I ever be able to do it again? ...etc., ect. "
Eh, thats what I do. I piss and moan until I can't write anymore. Then I've isolated what my writing block is for now, and move on to the PROJECT that I need to work on. Do this same excercise, but only concentrate on why you're having writers block regarding these lyrics, and making them fit to the melodies.
good luck