Create a Metabox that behaves Like a Taxonomy Box

I need to show all my custom articles on an archive page but grouped/sorted by subject.

So that the result is somewhat like

Subject A:

• A Sample Post
• Another Sample Post

Subject B:

• List item

A Post About Bacon

and so on?

I’ve read some related posts on here 17155 and 14306 and have come to the conclusion that this type of grouping must be done with post meta. However a simple metabox with a text input isn’t as friendly as the checkboxes of the category metabox…. nor the tag box with its (choose from most popular tags option).

So I am looking for advice, what is the best way to get the best of both worlds? I’d like to enforce selection into only 1 subject, but I’d like to be able to see what other subjects have already been used.

Can I replace the category metabox so that it uses radio buttons instead of checkboxes and then save the category info as post meta on save? where to start?

i ended up building a plugin that enforces radio buttons for any taxonomy.
http://wordpress.org/extend/plugins/radio-buttons-for-taxonomies/

for the project in question i will probably also save the taxonomy as meta. sucks that i need/want half the ability of taxonomy (knowing other available terms, etc), but need the sorting by meta.