I presume the the canister is filled with carbon but could you drill, tap and fit a drain screw to the canister and drain off any extra fuel and refit the screw after?
One time I over filled my RX300 and it started to drip gas under the car. I thought the tank was rusted thru but it turned out that the evap can was full because I over filled the tank. I spend a $100 bucks for them to tell me that I need to spend $700 more for them to replace my evap can (because I could fail emission and once the can is filled with gas its no longer useful). I just laughed at them and walked out of there.