Alright I think I found a way to do single phase soft start.
Hyper Engineering | Single Phase
But there are a few concerns.
Single phase capacitor start capacitor run motors use a centrifugal switch to control the start windings. If the voltage is too low or the starting load too heavy and the motor doesn't build up to speed fast enough to disengage the start circuit and it will smoke.
Also the armatures of induction motors are not designed to work in excess of 6Hz more time spent below about 3,300rpms will build extra heat in the rotor.
This soft starter appears have terminals for the start circuit so I'm guessing it's on a timer to prevent burning out the start cap.
I am still going to look for a cheap free used 2 or 4 pole 230v 3 phase T or TC 213 frame motor. Some times they scrap perfectly good motors because people don't know how to trouble shoot motors where I work.
With single phase I think I will only be able to greatly reduce start up inrush, cut it just about in half. Hyper engineering claims up to a 70% reduction in inrush and guarantees a 60% reduction.
I think it will take a VFD and 3 phase to mostly eliminate it.