Arggh, feel for you, bloody annoying.
Okay, my 2p-worth....
Option 1 - There are various plastic welding kits available for automotive use - IIRC, Frosts may do one, Eastwoods would be another candidate. If you have all the fixing points, albeit snapped off, with some time and care, you may be able to effect a fix yourself. Prob worth a punt for the cost of a kit.
Option 2 - When I had a minor spill on a GSX-R600 a few years ago, I took the damaged panels to an outfit near Theale, Reading, who specialize in working with this type of plastic and repaired it...so, suggestion being, to search for a motorbike plastics repair outfit, as it's probably the same type of plastic.
Option 3 - bite the bullet and get a new bumper. If its any consolation, my mates got a BMW 335d (E96), somebody was texting/radio'ing last week and nerfed him from behind, seemingly minor damage to the plastic (cracking and deformation), but BMW have quoted over £1,100 to remedy - they want a new crash structure fitting behind the bumper!

Thankfully the other guys insurance is coughing up, but by comparison, £350 is not quite as bad.
Hope thats helpful
S