Those passes are useless. We always fly J, and the old Premium terminal only had access for J/F passengers, so you could not guest there.
With the new lounge scenario, it looks like the same. Unless you guest someone into the Elite lounge, and then leave yourself and head off to the QR Signature J/F lounge.
I even asked QR in Kenya if I can give the passes to a colleague for them to use when I am not travelling with them, and the firm answer (after 6 weeks) was NO!