Not sure where the seat belt relay is located back there as my only need to pull out my cluster was to get at burnt-out bulbs.
That said, You can get the cluster out a bit more if you unclip the speedo cable near the pedal assembly...that should give you enough slack to at least have the cluster our far enough to rest the front of it onto the steering column.
It's still a tight squeeze to get your hand back there, but if you have slender, dexterous fingers, you might be able to get at what you need without having to disconnect the speedo cable...
