I think this is a terrible idea that only benefits your mechanic.
Non-original seats will detract from the value of your car. Yea, I read that you plan to hang onto the original seats in case you sell your car. But offering the car with race seats installed will lower its price (or cancel the sale if the buyer is accompanied by a wife). Including ratty, uninstalled OE seats in the deal won't add to the price. Sure you could re-upholster and re-install the OE seats prior to the sale, but if you are going to do that, why not do it now?
It isn't as if OE e9 seats are uncomfortable.