post-type index pages 'user templates'?

I saw the ticket and changes in 3.1 where custom post-type index pages are now enabled.

http://core.trac.wordpress.org/ticket/13818

Question:

I wanted to give the users the ability to switch their custom post-type index template between one with sidebars left, right, both, and one without. (I may also make huge template changes for each choice as well *small thumbs, medium thumbs, etc)

Normally this would be easy, as the user would create a new page and assign a template to the page.

However, using this script, when a user creates a page for the post-type indexes, it is going to go and use the archive-post_type-custom.php index page, no matter what template they choose.

So far I can’t even come up with a concept in my head of how to tackle this issue of giving them the ability to switch between custom post-type index templates.

Any ideas?