I definitely understand wanting to do something similar but those trees are significantly smaller than the one you’re considering.
No what I did is different than wedge cutting, I think it was herons bonsai on youtube where I saw it first. you effectively split the trunk along the vertical.
I was under the impression that wedge cutting wouldn’t work on a elongating species like spruce but I really have no idea, if it does then that would definitely be the way to go. But it’s still really hard to do correctly (or so I’m led to believe).
as far as ways to shorten the tree (other than going for some extreme bending) I know of three options.
One is to choose one large branch which will become your new apex and cut the trunk above it. You then bend that branch upwards. I know it seems like it would look dumb but after enough time it will begin to look more natural. You see this kind of operation done a lot actually. It’s one way folks make trunk taper granted it works best with deciduous species.
The other option for shortening is to air layer the top of the tree thereby essentially discarding the lower portion (or perhaps making a second bonsai out of it). This might be what I would try in part because I’ve always wanted to try air layering. As I understand it elongating species will work reasonably well with air layering but are harder to do than deciduous.
A third option would be to jin the top and carve it down substantially to make it look as though the top died and then broke off. It would take work and time to get the proportions correct but that could make for a really nice tree eventually. And spruce actually lends itself to large jins really well since they commonly do that in nature.
or hey maybe you could do both, air layer the top then jin the new cut off apex of the lower section.
I’m sure there are other approaches to take here but that’s what I can think of.