It's been done by our very own Orange4Boy:
http://ecomodder.com/forum/showthrea...tch-10028.html
And for the Subie fans:
Bobs Torque converter lockup mod (PhaseII 4eat/01 4eats) - Subaru Impreza GC8 & RS Forum & Community: RS25.com
This last one grabbed me in particular because virtually all of it translates word-for-word to work on my Forester. I can't tell if the 4EAT got bolted into any 09 Imprezas and of course the wiring might be different too, so YMMV. But you can see there are some possibilities.
For my own part, I would try to install a relay that depowered the TC lockup at the 3-2 downshift, so you couldn't accidentally leave the TC locked up at stoplights, for instance. It might become a tad troublesome to keep resetting the lockup, but how much cheaper is that against getting a new lockup clutch, especially when it permits you to skip gassing up for another day?
My Forester on its best day might break 24mpg. It's a great car when the snow flies, but man. It's thirsty.