That's a cool idea! I was having the same need -- to be reminded who hasn't paid all their fees or who still hadn't turned in all of their paperwork. My solution was to use the 'flag' field found in the bottom, right corner of the Member Window's Misc page.
I used a red flag for paperwork, a green flag for money due & a yellow flag for any other question. Then I included notes or questions in the Notes field. And finally, I made the 'flag' column visible in the check-in grid. It's close to the clabber's name, so hopefully as I'm checking them in, I'll notice that there is something flagged & if I need more info I can look at the clabber's notes. (which can also be shown in the grid, I think, or dbl-click the clobber)
I've never used the flags before, so I'll see how it well it works for me this week!