I am actually planning on giving a 650 to my grandmother for christmas, and when I saw this, I was intrigued. I just may do the same thing, but with a different cover style. I know you say your not particularly fond of the magnetic flap, but thats one of the things I am looking for in a cover, so that stlye will work perfectly for me.
For anyone else who may want to do this, there are many more styles on the
paperblanks.com website. (link filtered for the 5x7 covers with a magnetic flap)
I personally am fond of a very simple look like
this one. (hint, find the one you like on the paperblanks site, then search for the isbn number on amazon (or other site) to buy)