Another option I had forgotten about, URL Access:
Overview:
I want to say that I was able to test this using cURL or similar command-line utility to make a web call to SSRS and get the correct output from passed parameters. I can't remember, and if it did work I still dropped it once Enterprise Edition became an option.
If I had to figure out how to do your request, this would be the avenue I'd take. URL access report to a file, script add your filter, save it and email it to recipients.
This was not part of your oiginal requirements. This is a major ask. At least you got to learn a lot about SSRS 
@yosiasz Correct. I only found that the filtering feature has been promised yesterday. But yes I did learn a lot about data-driven subscriptions and it is impressive.
@robert_volk No forgiveness needed, my friend. So I've been able to give them 2 of the
3 requirements (excel file, emailed to dynamically-assigned recipients, but can't give them column filtering). I'll find out on Monday if the customer can live with that.
If the answer is 'No', I still have the option of using an SSIS package to save the output to an excel template which does have filtering, correct? I would appreciate a definite answer on that.
Thanks everyone. Let's forget all this for a while and enjoy our weekend.
No, SSIS output to Excel won't be able to add a filter either, unless you output to a file and add a Script task that does that, or some kind of add-in or template extension like: