So, like in real life, don't force current straight companions to begin a SGR. Make 1-2 new companion to be SGR for every class (I say 1-2 because all my chars only have 1 companion with allows romance -.- ). Don't touch what we have.
game they may be straight. In my
game, the female companions might all be bi or lesbian ! I'll find out if/when they introduce SGRs for current companions.