The axle is only 16mm. You could have one gundrilled, but a 3/8" hole drilled on the hex side would leave very little meat where the bolt head joins the shaft. It's possible that the bolt head could shear off. I'd kill for a hollow axle for the weight savings but I'd want it built differently.
I'm thinking you could have something like a shallow version of the exle pegs used on trick bicycles made up to serve as "cups" for your tiedown system? Or even a couple of tabs that would sandwich between the swingar and the bolt head with holes for your mounting system that are offeset from the axle.
Axle length is 14.5", give or take.
If this is your dealbreaker good luck with anything Japanese at this price point and road-legal made in the last quarter-century.