Here's an idea... (and keep in mind that this is JUST an idea)... you could try to replace the glass roof with plexiglass or lexan, it would be lighter (depending on the thickness)...

This would allow you to still see thru it and you would even tint it like the factory if you like.

On a regular tC, you'd have to make three pieces to replace the roof portions, ... on a Spec, you'd only have to replace one large piece...

Just an idea... my $0.02