@Horton right to me what you're describing is almost more of a rebound tester. You're sort of viewing the ski like a bow limb drawing it back and releasing it booooiiiinnnnngggggg and then you'd read like initial acceleration and how long it vibrated and at what frequency. Its perhaps less resonance than a simply a dynamic version of a flex test, what I'm visualizing would be to vary the frequency and map the ski which in theory would vibrate in different ways in different zones at different inputs which if we don't really have a clue what the skis are doing when they go bad or if they are actually doing anything then I'm thinking kind of like this, but upside down and at higher frequencies with less displacement.
Which is why I think avoiding the inserts is probably a good thing because you wouldn't want to damage it but you could fairly easily grab the last 2" of the ski.