Exactly Henrik, There is going to be power supplied to the motor when it's driven backwards (overrun) so unfortunately the relay idea wont work. It's also going to be run it at high freq PWM so would guess the IGBT would see a few thousand plus volt spikes before the relay made contact on it's first switching.

My idea of using a Fet to quench it out is not looking that hopeful looking at some datasheets, the Vgs is only around +-30V on some high voltage FETs. I suppose tho I could use some more complex circuitry to activate the FET

Gas discharge arrestors look like they might be too slow - their spark over voltage dramatically increases with dv/dt speed.

Maybe an LC quench between IGBT and Motor?

Thanks for your input so far guys