Ole has the perfect, if most expensive answer.

Now that I'm shooting 8x10 again, instead of 5x7 (my year long experiment), I've resurected my Linhof finder from a previous 4x5 Technica purchase and carry that around to preview from different angles. Given that my 8x10 equipment weighs about 45 lbs., this is unbelievably liberating.

The finder has a real zooming optic so near/far relationships, e.g., telephoto compression effects are clearly shown in the viewfinder. This is something a viewing card won't do.
Take care,
Tom