ES300MM

I have the CEL and Trac off lights and only getting code P0440. I have replaced the gas cap and reset the code 100 times and it keeps coming back. Does not affect drive ability at all. What typically goes wrong to cause this? Also are there any hacks/bypass procedures to make it go off? I live in Kansas and we don't have emissions testing. While I am a bit of a tree hugger I don't really want to spend $250 on a new charcoal canister simply to make a light bulb go off on the dash. Any suggestions would be appreciated.

2000 ES 300. 199K miles.