Add another spring ... The key here is keeping the symmetry of the springs , you'll find space to put up to 5 springs in the back of your bridge , usualy the factory setup is 3 springs (1 on each edge , and 1 in the middle).
So if you're putting in 4 springs , have them on the edges , so that the middle one would have no springs. (I hope that wasn't confusing!)

I think shortening the springs is just a joke since a brand new one just cost 2 bucks .