OK, if you also put $parsedtext = '' at bbcode_parse_start (as well as $dosmilies = false, both inside some if condition I'd assume), and also put $post_cachable = false (ETA: at showthread_post_start, that is) (probably inside the same if condition), then it seems to work. Well, at least it turns smilies on and off depending on how you set $dosmilies, but I haven't tested to make sure it doesn't affect what other users see.
Another thought was to somehow make a style that has smilies turned off. The caching stuff seems to be separate for different styles, so that might eliminate that problem.
The style idea is excellent... will look into that... thanks. :up: