Catch Event For Specific User Promotions Job

[sigh]

We currently offer paid and free memberships on our board, and new members get a free trial of the paid membership access.

I have a user promotion job that checks for members in the Trial usergroup and demotes them to the Free member usergroup after the number of trial days (currently 3).

I would really like to be able to send users an email when the system downgrades their account, reminding them that the trial is over and enticing them to upgrade. I've tried poking through files and looking for hooks, etc, but this seems a little over my head.

Can anyone advise me on how to run something specific (call to the autoresponder email service) when a user is demoted by the User Promotions job? I'm also willing to pay a knowledgeable programmer to set this up.

I'd also like to email users when their paid membership expires, but I'm guessing that's a separate issue.