I don't find the flipper gap to be an issue. What is an issue are the cheap SDTM drains that comes from the center lane/pops. Those would drain even without the gap.
What would solve it is the placement of a one-way gate similar to what is already on the Ecto lane. I've pulled that one off and measured it on the center lane. A properly constructed one, with the attachment mounted on the right, would fit perfectly without interfering with Slimer. At least on the Premium/LE.
That way you could make the Gozer shot just fine, and when the balls rolls down the lane, the gate stops it, and it rolls out to the left.
No more cheap SDTM drains.