You kid, but I thought about it, albeit for all of about 3 seconds before I remembered how uncomfortable and hot a Vader helmet gets. It doesn't quite fit anyway, but almost.
At the moment I'm working on getting a head strap inside. I was gonna use one of those real nice lookin hard hat suspension webbing liners people use for Storm Trooper helmets but there's no real way to fix it to the inside of my thing. So I'm just gonna use an on old welding mask one because it's got those two handy screw points on the sides. Planning on making a few holes so I can choose and adjust it, if shoulder armour should get in the way. Then it's onto attaching the helmet to the mask, which is gonna be tricky to set up and check it's placement but I've noticed Vader helmet helmet-to-mask angles vary.