Corsaire, I have a bad lower back and the same trouble with hills ... you have my sympathy. What I've been doing is for the last ten weeks I've been going out every Sunday morning and doing hills. Big hills, long hills, lots of hills. Takin' my time, not worrying about cadence, speed, heart rate, whatever, just spinning easy up hills. Gradually my back is getting stronger (I can do a sit-up now for the first time in twenty years), the hills are getting easier (not easy, just easier), and I'm nothing like as sore when I'm done. Oh, and stretch before and after. Seriously.
Keep pedaling and g'luck,
Jen