Custom plugin: changing $_GET vars to permalinks?

Hey guys

I.m in the midst of massively overhauling a custom plugin I did for a friend. It manages and lists theatre shows and is included via a function call inserted into a custom page template. On the front end the results are paginated and you can filter them, so:

http://www.thesite.com/performances/?filter=comedy&page=2

…shows the second page of shows that are listed as ‘comedy’ (where ‘performances’ is the page permalink). This does not use custom post types or anything like that, it’s all self-contained in a single plugin file.

What I’d like to do is have those query parameters appear as pretty permalinks, so it’d be more like:

http://www.thesite.com/performances/comedy/2

I’ve seen references to the (undocumented) hooks post_link and pre_post_link, but they seem to apply more to custom post types. If anybody could shed some light on this for me, I’d be most grateful.