Ok, 2 things...
First off...if a 95 recast doesn't fit your big ol' noggin...what makes you think a 95 vinyl will fit any better?
If your head is that large, it sounds like you'd do better to just spend your money on one of the many and various larger and nicer helmets offered here on the TDH.
Personally, I've never understood why anyone here would bother with the DP vinyl helmets. I guess I can understand if you're on an extremely tight budget...but a Fett costume is an expensive and labor intensive project now matter how you do it. If you're serious about your costume, you can do much better than a DP.
Just my .02
However! In the interests of community and helpfulness...I do have a suggestion.
If you're intent on using your DP, you might try using a spray in-liner on the inside of the helmet. RA does this on his vinyl conversions. I believe its the same spray that is used on pickup truck beds. You spray it on, and it hardens, thus reinforcing the inside of the helmet.
So you might wanna check your local automotive shops.
Hope that helps.