I'll echo Slip. Using soft start mode on a VFD will be the easiest way to go. You may be able to run a VFD 3ph to 3ph with input from your generated power off your rotary.
The next easiest option will be some sort of slipper belt arrangement so you fire up the motor with no load, then clutch the machine into gear using an idler to tighten the belt. Put a big, old, badarse looking amp meter on the line and watch it as you pull it up to speed to keep things under control.