This diagram will help visualize what I have in mind.
The addition of the extra IGBT has two functions. If the converter ever goes offline for some reason, the current will flow trough the IGBT diode into the inductor and closes the loop to GND. The same happens if that particular switch shorts (shorting the primary would make smoke as mentioned).
The orientation means a standard half bridge could be used, so it would simplify the design, with the center point attached to GND via an inductor and the negative attached to the DC-Link as the motor IGBT's. A 4 IGBT approach as per Paul's idea, but requiring no other extra components, other than the inductor.