Wow, a lot of good ideas for spring removal here!
I did not make a tool for removal of mine (they are the heavy load ones for the NASA hood).
I removed the hinges from the car an put them in the lowest tension position. I hooked them up with two steel ring chains between two apple trees behind the house. I started to twirl the chain with a screwdriver to shorten it and give the spring a pull.
This even worked better with a block and tackle type hoist instead of the twisted chain. The springs are simply pulled between the trees and the hinge falls off when they are unloaded.