Only option I can think of is to find a donor car with T-tops, and have a body shop swap em' out. Seems to me it'd be better to just keep the Esprit in original condition, though.
 
Another option is to find a later model Firebird or TA - like a 4th-gen - that already has them. The '90s models are sporty as hell, and pretty affordable these days. I just bought a base '94 Firebird pretty well loaded for $925 for my daughter.