I'm wondering the same thing! It seems like you could use the triple clamps from the R NineT Classic that has upside down forks as a starting point, but you'd need longer forks. I have the Wilbers +70mm fork kit (which only increases travel about 30-35mm or so), but it's nothing like the proper USD forks I have on other bikes and I'd be keen to upgrade if there was a decent path to do so. I was thinking to start scouting around to see if anyone has worked this out. I found a post of the Classic upper fork tube outer diameters so I've got something to start with. Part of the issue is being able to fit the original front wheel which I'd really like to do as it's a nice tubeless design.