I just got a set of these and I think they'd be pretty good for riding.
The fit is really good (for me) and the low profile is AWESOME. I just tried it with my helmet and I don't get the squished earphone against my ear akwardness.
Relax the kids, the picture is from the internet.
As you can see, the IEM body kinda fits into your ear shape like a custom mold, making it really low profile.
Sound isolation seems pretty good too but I haven't tried it on bike... I'm guessing it would be OK but ear plugs would still win on that front.
Anyways, just throwing that out there in case anyone's looking for something that might work, most headphones stick out too much but these are awesome for fitting under the helmet. Detachable/replaceable cords, $100 on Amazon / eBay and easier to find than anything custom or esoteric. Peace!