Come on Rolando! You are good at customizing. You don't need help. Just pop off the helmet and you'll know what to do! (dremel away all the ridges and glue back the helmet. That's it!).
***** UPDATE *****
I copy-pasted these brief instructions that I posted at Rebelscum. Hope it helps:
"You have to shave all the ridges that are on the inside. Shave also the glue spots, you will have to apply glue later on them when you are done. All this shaving of the stuff inside will make the dome deeper and have more room for the head. I did snip the peg a little bit and dremmeled around it so it would go deeper into the hole that's on the head. Also, I didn't feel it was necessary to widen or "flare out" the helmet. Looks good as it is. Finally, use strong glue on the old glue spots, place the dome back firmly and let it dry. Hope this helps."
Don't go too low when you position the dome. Go more or less like in this picture: