Create a blueprint with a skeletal mesh. Then just place your Nanite static meshes under that skeleton in the blueprint hierarchy. Use the Parent Socket attribute to choose which limb its attached to. Regarding the pains-taking nature of the proces, you can probably automate it with some scripting, depending on how many characters you need to set up this way. Or just bite the bullet and do it by hand.
Here’s a jank-tastic version I quickly roughed up:
