Limit Upload Space for Free Sites

I have a WordPress multisite installation with Pro Sites and it’s Upload Quota module. I understand I can limit the upload quota for Pro Site levels, but there is no way I can limit that for free (non-pro site) sites. I tried setting up “Max upload file size” under “Upload Settings” in Network Settings but that limits seems to have been enforcing over my Pro Sites upload quotas. Is there any way or custom code that I can use to enforce an upload quota on the free sites? Please advice.