I bought one of the Tablet PC Slim pens as a backup for my PE stylus a while back, and I can confirm it fits into the slot just fine. For those who want a comfy, full-size feel, it ALSO fits quite nicely into almost any 0.7 or greater mechanical pencil that has had the guts removed. 2 caveats:
1)You may need to grind down the tip of the pencil a bit (or rotate a drill bit around inside it a little) so the stylus tip will clear the barrel, but 'tisn't hard (obviously don't do either of these things with the stylus already inside the pencil casing).
2)Don't use a mechanical pencil casing with a metal cone at the tip. When I tried it, it interfered with the use of the pen on the e-ink side. My suggestion is to stick to plastic.