A few more thoughts: (warning! not all of these have been tried. At least not by me ...)

A PGP F3A Lightwall 30mm wing tube to replace the EPS filled tube that comes with the plane. (~ 1 oz)
Corrugated Nomex servo tray (use the fibreglass skinned version if you use a 2.4 Ghz RX)
Carbon Fiber Spinner from NetBox Hobby (~ 3/4 oz)
Shorter Bolts (~ 1 gram)
Custom fitted servo extensions that don't have any excess length
Bolly Carbon Fiber Gear, and Wheel Pants (~ 1oz)
Titanium pushrods for ailerons and elevators
Eliminating the receiver switch, and just plugging in the connectors when you want to fly (~ 1 oz)
Dubro Plastic Clevices with Brass Pins
300 mah Li-poly RX battery with regulator (~ 1oz)
A high voltage BEC to replace the RX battery entirely (~ 2 oz)
Half Height Servos for Ailerons (~ 1oz)
Use a 21 X 14 APC prop instead of a 22 X 12 APC prop (~ 1oz) (for Electric Version)
No internal ducting (for Electric Version)
MK plastic Tailwheel
A 4350 mah 25C battery (for Electric Version)
Shorter Wing Tube
Shorter Stab Tube