It can be done, but I don't have that knowledge on these complex new safety systems. If not for our lawsuit crazy society these wouldn't be necessary, but the manufacturers' have to reduce their liability any way they can. I've been mowing for over 50 years on tractors, both lawn and brush mowers, and while I've known farmers to fall under brush hogs, I have never heard of anyone hurting themselves mowing backwards for a few feet. Certainly my ZTR mower lets me mow backwards. If you couldn't you'd lose a lot of productivity.
Similarly, this board prohibits members posting instructions for by-passing the safety mechanisms. Perhaps a knowledgeable member will see this and PM you with a "how to" or "where to look for help".
Good luck with your issue.
PH