[mb-users] Box sets of existing releases?

I've recently acquired a box set consisting of 8 previously released
discs, some of which are already in musicbrainz. Is there a sensible
way to handle this at the moment, or do I have to manually create a
new release group and release with all 8 discs in it?

(Ideally I guess each CD would be a new release in the existing
release groups, and then somehow the box set would tie those all
together? But currently I think a release can only belong to one
release group?)

The discs are in card sleeves and don't have individual barcodes, so
they would need to be a separate release from the original individual
releases.

Cheers

David