I would echo the other people about taking the full lane, but I can see that a long uphill start would complicate it. Although I always take the full lane at stops, I will often start to drift back over to the right about halfway through the intersection, if the person following me is leaving me enough room and it is clear otherwise, as sort of a signal that I'm returning back to my "normal" (in their viewpoint) position to the side and they can start to think about passing me again.

Perhaps you can do something similar. If you are stopped, as you were in the situation, take the full lane, and stick your right arm out as a turn signal long/often enough so they can't miss it while waiting behind you. (Other threads here have discussed the relative merits of the official right-turn signal using the left hand raised, versus just sticking your right arm out. The latter is more intuitive on a bike and seems to be favored on the threads I've read, so I do it too.) When the light turns, your waiting behind the car in front of you hopefully makes it clear to him (her) that he should go on, while the cars in back of you should have a clear idea that you are turning right. If/when it appears that the cars in back of you are ready to go faster than you are laboring up that hill, you might move to the right if it feels safe to do so. In a way, you're lucky you're turning right; a straight-away would be harder in this situation.

I also find a mirror to be helpful in keeping track of the situation behind me.

Hope this helps.

- John