There is two ways to do it, and I have done both...
First, I cut a two feet graphite blank and insert it into the butt section of the 9 weight blank.
Second method is just finding a fighting handle to fit into the Fenwick 909 vintage rod (in the video). The actually length probably only 9'8. To make sure it is a tight fit, I use electric tape to tape the fighting handle first and screw it in very tight... if I want, I still can remove the fighting handle.
so, I ended up getting an FF909, but without the fighting butt. what do you guys use for an extension....and yes, the sole purpose was to make it into some sort of switch rod with an emphasis on two handed casting. I also ended up getting a cheapo 11' 6/7 switch rod off of that one auction site...it's a pure joy to cast two handed, scandi style (that's all I've been able to figure out so far)...but, that's pretty much what I had in mind for this Fenwick.
The Fenwick 909 did not come with the fighting handle. The fighting handle I have was from another Fenwick rod 9310 - 9'3" 10 weight salmon rod.
I simply insert the fighting handle to the 909. http://fiberglass-fly-rods.pbworks.com/Fenwick
sorry for the confusion.
I was just a spectator too until today! while its a little frustrating learning to cast all over again (single hand and spey are black and white) it was really fun to nail the snap T a few times on the pond behind pacific fly fishers with some great instruction from joe.