You should be able to just bring your guest into Diamond and after you check
in you leave, and your guest remains. I've done this numerous times,
including at Paris where I just told the check-in person, my husband is staying
here while I go to play - bye.
Another gambit is to talk to a host and see if they can arrange a "guest
pass" for your friend/partner. I've been able to do this at least once, and
they wrote up a special pass so my guest could go in and out of Diamond Lounge
all weekend without me.
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