Hey Skater-welcome.
I've attached a
Petzl MYO XP to my Giro Pneumo. The rear "vents" of that hemlet keep the lamps strap in place, and I use 2 "zip" ties on either side of the lamp portion to keep it stable. No problems with it "flopping" about or anything on a 300K ride last weekend.
The "zip" ties I use are very low break strength-just in case I happen to have an incident involving gravity (and my head). The lamp will break away. Now I have no idea if this voids my helmets safety rating or not-but having the lamp there in the first place offers a lot of "being seen" protection. This gives me the ability to point it directly at drivers eyes when I can't be sure that they have seen me-folks who may have attempted to turn in front of me in paticular.
I just took a look at my Atmos, and my lamp will easily fit with a similar setup (zip tied in front). One way to make "break away" zip ties, if you can't get any low strength ones, is to cut a small notch or slice part way through the zip tie once attached. This will take trial & error, but worth it from an added safety perspective. Should you go down (stressing "should")-you'd want anything attached to your helmet to come off--and away from your face.
I also have a
Planet Bike sport spot 4 LED (in blink mode)-attached just above the Petzl Myo--as a passive "be seen" light. This light has a small strap that wraps between & around vents, but the light itself attaches to the strap with a plastic "quick/slide" release. This lamp is an excellent one "to be seen", but not enough light to see with.--I picked it up on closeout for a third the price listed at REI.COM (seems there all out). This model also can be mounted on your bike. I had this light mounted to my handlebar, in steady mode, to meet the legal requirement (a white light must be mounted to the bike)-on last weekends ride.
--You might get other (better) headlamp ideas by moving this thread, say to advocacy&safety-or perhaps even to the Commuting forum.
[EDIT] Added pictures of my setup (on my Pneumo), with and without my rain cover-and with the MYO XP on in daylight (camera flash used):