No. The line which goes up front, and originally connected to the carbon can system up there IS THE VENT and MUST BE open to the atmosphere
...........at least if I understand what you are trying to do. If the tank has a dedicated vent line you need to use that for a VENT and it must go up high to prevent siphoning. This is why the 69/ earlier system with the vent "teed" into the filler tube worked so well. It was almost impossible to create a siphon situation with that.
Only situation I can imagine is that EG you filled it VERY full with cool gas, then parked it with the filler on the downhill side of a very steep hill.
Even then all they would do is siphon down enough to create a space in the filler neck and then "break" the siphon.
