I know in the past, I have installed them on the control surface, then, WITHOUT epoxying the fixed side, just slide them in a little ways into the existing holes on the stab/rudder while they are turned 90 degrees to the control surface. It ensures proper alignment and allows you to glue only one side at a time, which I prefer to do simply so I can ensure no epoxy seeps into the hinge area itself. This method also ensures that the hinges themselves are on the same pivot axis, since if one hinge is glued deeper in the control surface than the one next to it, the pivot point can be off a bit. this eliminates that issue.

Just my $0.02

Dave