Drill a hole into Fuel Filler Neck?
Also, I do have a vented cap on the car for those inquiring minds.
Not all vented caps vent IN, some just vent out so be careful with that.
If this were me, as someone who has installed and ran 100 fitechs....
I'm assuming you don't have a vent running to atmosphere on the fuel sending unit in the tank? If you do, then thats your atmosphere vent, so you just need the FCC Vent/overflow (which you described perfectly) somewhere ELSE back into the tank...like the BOTTOM of the filler neck, which you should be able to carefully remove w/o hurting anything at all.
If you don't have a vent to atmosphere on the fuel pickup, then remove the filler neck, put the FCC vent on the lowest spot you can on the neck, under the trunk, and then add another barb to the top near the filler. Run that one back out of the trunk, and into a framerail or something. Bottom barb/line will be adequate for the fcc fumes or any "burp" fuel. The top will vent to atmosphere and safely expel fumes while allowing venting, back out of the tank.
done
