As a follow up I tried the first suggestion. These were perfect, the dampening isn't so much that I can't hear anything, which is good for hearing out my tiny 250 engine, but enough so that the wind noise from my helmet is reduced to a whisper. The stems never dislodged when putting on my helmet but that might be a per individual problem. They're comfortable to me but I've never had to ride for more than an hour.
I rode with these for the first time today and I have to say, I had so much more confidence on the freeway without that booming sound in my ear. I'm a believer. Earplugs are a must for highway speeds!