I ended up doing it like this.

I ask my clients to create a file called mobile.php on their server. I provide them with about 7 lines of code, that CURLS the appropriate page from my server. The file also sends along context information, so mobile.php now functions as the complete mobile website. I then provide a javascript browser detection script. I do this with javascript, because this will be compatible with all other sites.

It may not be the most efficient way, but it did the job, while still honoring the requirements I wrote in the first post.