I searched for countless hours for something like this, I really hope the next book has a better tablet portion with stand alone accessories. I understand that you said you weren't looking for a full sleeve but this is the one that I got:
It's really not that big and I put just the screen portion alone in it when I go to meetings that I may need to take notes in, has a pen loop on the inside, and a nice little pocket in the back that I keep a microfiber cloth in to clean my screen when needed. It also fits the entire laptop if you plan to take the keyboard with you, though I hardly do that as I use a briefcase when carrying the entire device. The magnetic flap works great and I have never been worried about the clipboard falling out out even though there is a little wiggle room. Cheap, high quality, would recommend.