Getting back to the original issue
while people predict gloom and doom if the companion tries to fly without the primary, I forget whether the reverse is true.
i.e. I can't imagine they'd care nearly as much if the primary tried to fly without the companion (although presumably all downline companion segments would still be removed).
_If_ that is case, and if this is the best candidate for using the certificate (i.e. if it doesn't make sense for you to hold onto it for some other opportunity) then unless OP is counting on every MQM, there is nothing that says the cardholder needs to be the primary, -- you could try book it with the other person as the primary traveller on the reservation, and OP listed as the companion.