As I said in https://salsa.debian.org/salsa/support/issues/88:
Diving into the binfmt docs a bit, it seems to me that the binfmt registrations are just a lookup table of sorts that provide a path to an executable based on magic or extension rules. So if the container host has all the relevant rules in place, shouldn't the container itself just be able to read them and use them? That could be achieved either by installing packages like jarwrapper on the container host, or just by echoing the binfmt rules to /proc/sys/fs/binfmt_misc/register in a startup script.