Screen pop a report that uses "in list" filter?

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(Sorry for cross-posting with Service Console - not sure if people read both.)

I've created a report that searches for contacts using the "in list" filter. (contacts.c_id in list ......)

It works fine when I run it in the console. Now I'm trying to invoke it using a screen pop call, and it doesn't behave as expected. If I invoke it with just one contact ID, then it works fine, so the question is how to send multiple contact ids in as part of the screen pop URL.  I've tried a few variations of the URL, and nothing seems to work - the report just comes up empty or has errors.