Another thing that helps is to learn the end of one verse and the beginning of the next as a (non-rhyming) couplet, so that the first line pulls the next one along with it.

Another thing to do is just repeat the last line or the last verse until the correct one comes along. Or sing nonsense syllables till you come to a line you know.

And you can have a tape of yourself singing it, and play it as you are driving along, to push it into your head. You know the way, when someone else is singing, you find you know the next line - well, this is a way of using the same mechanism. It can sometimes work.