Sorry, I don't have a proven fix for you since I haven't even gotten mine installed yet (I'm in the market though). Maybe just good ol' 3M tape to the inner edge would do it. Seems to work well enough on the outside which is actually in the elements.
I just went to Pep Boys today to check on the in channel Vent Visors ($61) for my Mega. The catalog had other brands available for order EGR, Wade, and AVS?
Does anyone know if one brand is better than the others overall as far as installation, color fade, strength/cracking, etc? I've heard WeatherTech but don't know how many different ways you can attach an "in-channel" that would make em hold better.