A simple idea really. Make it so that some topside stores (like the grocery store) will only sell to you if you are a corporate citizen. Any corporate citizen, not just megacorps.
In terms of food... You can sort food by theme and create an extra level of difficulty for mixers to get that fancy good food. I'd also try to consider ingredients when sorting the food between stores.
Can do similar with other stores if desired. This in general might promote RP as a mixer would have to work with a corpie (probably on the down low) to get some premium items.
