Not sure if there is a proper way but you could probably loop through the tree and find all the ones that are placeholders and preload that way. Saves some typing.
If you mean in during runtime it wouldn’t work. Preloading requires a constant as the path. It has to know the path before the script executes in the tree.
I’m hoping for some built in option that I may be missing that will put this path information into the scene file for me.