The solution? PCs. As usual, we want to see PCs be proactive here. Have your corpie PC act the part publicly even if they secretly love the mix or particular mixers. Have them make life hard for any Service Mixers spending too much time topside. Make life hard for any Corporate Citizen seen to be openly associating with a Service Mixer.
Have your PC be loud and pushy about it. Be the rich, entitled, classist antagonist that calls the Judges on Service Mixers for minor or non-existent problems. Have them report these things to bosses and gossip about the liaisons to co-workers. Collect data the launch smear campaigns against them - especially if they aren't from your corp.
Openly treat Service Mixers like second class citizens and be ready to make their life hell if they try and buck you. Literally order them about like servants or briskly dismiss them from any conversation they try and be a part of with other Corpies. Bluntly point out their lack of status and worth at every opportunity.
Lead the way and be the reason why Service Mixers find living topside just as bad as living in the mix though for different reasons.