I have filled holes 3/4" dia. in bike fairings with abs cement and some grated abs.

if you have repeat cracking issues you may need to ad some hot staples to reinforce the repair. 

I have a similar project on the bosses E60 when it warms up. Since she insists on backing straight out of the driveway and hitting the bumper on the curb every time.

RobZR said:

If you find all the pieces, it can be welded or glued together. I did both on an back bumper.  Welded it to hold in place and then use ABS pipe cement to glue it and ad reinforcement. 

https://www.menards.com/main/plumbing/rough-plumbing/pipe-tubing-hoses-fittings-accessories/pipe-cements-cleaners-primers/oatey-reg-medium-abs-cement/309992/p-1444449932067.htm?isQubitRecommendationsAvailableContentDescription=true

Basic welding

Just don't inhale.

Noted. Looks like a ~18 inch chunk from the pictures he sent me, not sure if it all came off in one piece though. We'll probably try this if we can't find one by spring, I told him that there's no point in repairing it immediately with the chance of it happening again.

https://www.menards.com/main/plumbing/rough-plumbing/pipe-tubing-hoses-fittings-accessories/pipe-cements-cleaners-primers/oatey-reg-medium-abs-cement/309992/p-1444449932067.htm?isQubitRecommendationsAvailableContentDescription=true

Basic welding

Just don't inhale.