There is a pocket at the front edge of the rear seat , down by the floor, that has an allen wrench in it that is for cranking the belts back. Each B-pilar has an acess hole at the bottom for cranking the belts back. If you pull the trim panel off of the b-pillar, you can unplug the belts motor. Then just use the "emergeny" release button and pretend you're hooking up a 2 point harness each time you get in.
Found this post from 2007 by going back to google and typing in 1990 Subaru automatic seat belts. When I tried the same search on the message board, I got nuthin'. Don't the archives go back that far?
Anyway I did both cranking and unplugging and now I have 2-step manual seat belts, and I'm ok with that. Took about 10-15 minutes and I'm happy. Always hated those "mice" belts.