Due to staffing and safety issues, I doubt you can get a tour.
The only thing I have ever heard about for sponsor company employees is a special lounge with soft drinks and a back door to the attraction.
I know that there is one at Mission Space for HP(?) employees and there was one at Test Track that is now closed, but I have never heard of one of these lounges at SM.
DH is a FedEx employee and we were able to utilize the Space Mountain/FedEx lounge in October 2000. It was an air-conditioned room with chairs, sofas and free drinks. We were also led up to the ride thru the back/exit with no waiting. Very cool - wish they were still sponsors!
i'd really have to imagine that benefits afforded to the employee of a sponsor would be lost when the sponsorship is abandoned, but I guess anything would be possible.