If you're trying to prevent glare on the screen, you could use an LCD viewfinder. Of course it makes it harder to see the screen from certain angles without having your eye placed directly into the Loupe. In these situations, maybe a simple sunshade or LCD hood would be a better choice.
I've seen the folding plastic pop up sunshades for mini LCD screens, but I haven't seen anything quite like these Vello Mini LCD Hood Sunshades. Looks like it just folds over the flip out LCD on your camcorder or DSLR (with swivel screen) such as the Canon 60D, T3i, GH2, or even the new T4i. Available in 2.7", 3.0", and 3.5" inch LCD screens via B&H (Click Here).
Vello Mini LCD SunShade for Vari Angle LCD Screens
The Panasonic GH2 and Sony NEX-5 have a 16:9 LCD aspect ratio, while other cameras are 3" or 3.2". If you've been shopping for an LCD loupe to fit the GH2 or NEX-5, there really wasn't much in the 16:9 aspect pool (except for one that ran over $120 dollars). Here's a new loupe that claims it has been designed to fit those exact 16:9 aspects providing shade out in the bright sun to check exposure, or used to magnify your LCD to help you get focus. No sticky frames, no diopter, no base plates, just mounts with simple bands. Pricing is about average for a DSLR LCD loupe.