If I were using the upside down (or better, hung) bike as a truing stand I'd skip the zip ties and simply use the brake pads. I'd adjust/push one pad to near touching and go from there. And yes, wheel flips to check dish.
All of my early wheel builds were done on hung bikes. Started ~1973. Got my stand in the early '80s. So every wheel I raced until I started working in bike shops.
Biggest challenge for my bikes as on-the-road truing stands is the handlebar setup. I use nice and very long stems. They don't grow on trees. I also mount my brake levers low, like racers 50 years ago. Upside down bike sits and rocks on those beautiful stems unless I set the handlebars on blocks. (Using pista-like bars with generously rounded "shoulders" and the bars rotated down doesn't help either.)