I try to never use a spring to open the lid if at all possible. As Fred said, it takes nothing to torque a pb lid to make it spring open. If well inlet, you'll never see any surface deviations. It really doesn't take much of a bend/twist to make it work.
My method for a hidden pb release is to inlet the toe plate using 1/16" brass, then drill the hole to the pb latch. Once it's set up and inlet, I file the inside of the toe plate to make it quite flexible. Youy do't need to do the whole toe plate, only the part you want to flex. Occasionally, you'll need to deepen the inlet wher the flexible part is. What I like about this, is that it adhere's pretty close to the KISS principle.