The seating guy I saw pointed out this 4 point rigid mount :
Lite Mount (pictured at right) - fixed hardware for a rigid mount that adds only .61 lbs. - down the page on the Jay J3 page : http://www.sunrisemedical.com/produc...jayj3back.aspx .

I have to tell him about ChesBay's concerns and ask about the Spex backs and see what he says.