If you don't mind the hassle of finding a pin or spike, then I'd get a flush mount zerk fitting for a nozzle type grease gun and mount that. They're a much smaller fitting (less likely to get hit in a shuttle or trail situation and broken) and require a much smaller tapping hole (less compromise to the fork lower's strength). You just have to depress the spring loaded ball bearing with a pen or a small allen key or multi-tool screwdriver to relieve/equalize the air pressure inside.Maybe You can put it on the bottom of the fork leg (it is the thickest part of the casting)? Drill a small hole and tap it for a schrader valve core? Put the bike up side down and just press the valve to burp the lowers.
Plus, if mounted in the area between the seal and foam ring near the top of the lower then you could use it for it's original purpose and squeeze in a bit of slick grease afterwards.