Well, Ryan (cameroz1985) helped me with the last piece of my puzzle... I'll be ordering slow-recovery memory foam (the stuff disposable earplugs are usually made of) to fill in the speaker-pocket area of my helmet. The idea is that it will protect my already-bad hearing AND allow me to hear my kit better while making it easier to get my helmet on. I currently have the speaker pockets stuffed with crinkle-free facial tissue but the earcups pressed against my head fold my ears down when putting on my helmet. I can just correct this with my glasses, but being able to just push on the speakers just before sliding into the helmet will be much less trouble.
Oh, and FWIW, I uploaded a quick little Parrot SK-4000-related video to YouTube today...
Link to original page on YouTube.
Just a little nit-pick. I'm saving the interresting stuff until I have completed my custom helmet. 
After the first pair from eBay arrived with a URL for more, I actually ordered a couple more sets of 50mm earcups because my sister's dog shredded the foam on my Sony DR-BT22 Bluetooth headphones and they happened to fit perfectly. Now they look and feel better than ever with less distracting noise, though I had to hide the chew marks in the plastic band with electrical tape. 
Oh, and I had to run a bent coat hangar wire piece along the inside of the folding band and basically removed the folding feature.
One of the ear loops on my old Logitech Freepulse heaphones (also A2DP Bluetooth) was stretched/loose so, even though it looks funny, I threw the extra ones on those and asked my sister if she prefers them with or withoout them. She chose "with." *shrug*