There is always going to be a small (almost invisible) contact point. You're going to have to rack them using small inside clamping wires. 1/16in Ti wire works well, and is not too expensive. They can be bent tightly and handle a hole size if slightly over 1/8in.
For holes smaller than that, I suggest using 1/8in rod smashed flat with a hammer, then ground to kind of an arrowhead shape. These can be wedged tightly into smaller holes.
For threaded holes, use a die to thread the end of your wires.
This pic shows a bigger size, but you get the idea:
