just thought of this, this morning and it works great, run a dowel thru them, it will allow you easily rotate the part as you paint and will keep most overspray off the inside of the axle hole
Your hack brings to mind the countless 'Redneck Rotisseries' constructed with simple materials. This is a CJ5 frame set up for sandblasting and painting but the same concept can be applied to a go kart or minibike frame.