The "bumperettes" have a bit of absorption, but it wouldn't take much to transmit that energy to both the upper clam and the lower diffuser. They pretty much look like something to appease the DOT. I fail to see the point of them myself.
After much mental wrangling, I am going to try to use what I have to fabricate a new rear grill. I'll post pics if it comes out, otherwise you'll never hear about it from me again.