Acton makes a pretty nice head rest that clamps to the roll bar.
I bought one for mine. The roll bar on mine has a bolt in the perfect spot to give me an extra unwanted skull orifice.
http://actoncobra.com/index.php?main...roducts_id=237
There used to be a guy who made cheap ones out of plastic and plywood for the FFR mk3- held on with velcro.
Not as pretty, but they came off in 10 seconds.
The acton one is rock solid, and just about perfect position for me as a usable head rest.