raspbmirror.py - how to specify preferred mirror?

[annuello]

I am trying to set up an internal mirror site in a somewhat firewall-restrictive environment. My machine running the raspbmirror.py script has access to only archive.raspbian.org, mirrordirector.raspbian.org and one geographically-close mirror site. The script spends considerable time trying to download from non-accessible mirrors which eventually times out and another server is attempted, but it becomes super-slow just waiting for timeouts to complete. I think mirrordirector is suggesting a different geographically-close mirror, but alas my machine does not have access to that mirror.

How do I nominate/prioritise the mirror site that it can access? I've tried using the baseurl and mdurl params to point the script to my preferred mirror, but that fails.