How to set per-site php config in a mutisite configuration on IIS 7?

I have a working multi-site configuration running on IIS 7.

Now one of the site admin wants to bump the max_upload_size for his site and I'd like to not do that for all my sites.

I searched multiple times but I can't find a way to do it since adding the 'ini_set("max_upload_size","96M")' to settings.php doesn't work.
I read about changing the .htaccess file but I'm on IIS and I'm not sure if it has an equivalent...

Any thoughts?