I doubt this is going to work actually.
while I know it’s possible to air layer ezo spruce, it generally takes a long time And it’s not very reliable.
you say you will separate in 2023. Perhaps by 2023 it has Grown roots however, here there is no longer foliage available to support the existing roots.
when you do a layer that requires a long time I think you need branches below the layer that can support the existing roots. Otherwise those won’t survive for 2 years.
That's an interesting point.
I guess the exception would be if there are other trunks/branches not being layered that are still being supported by the rootstock?
I currently have two layers in progress on a home center shishigashira that's grafted. They're actually stacked on the same trunk right above the graft union. However, there are two other shishi trunks (stalks) still being supported by the rootstock. All of the trunks have continued to grow throughout the season.
Both the air layers are filling up with roots, although I will admit, the top one with way more foliage is filling up quicker.
I've posted a pic to illustrate what I'm doing.
I guess the big difference is maples take very quickly. I'm planning on removing these ones sometimes after they go into dormancy. The top one for sure.
Anyway, I hope it works out for you OP. At the very worst maybe you'll get some rooted cuttings out of it.