Tracking multiple results (array) in a single custom variable slot

We have the situation where we want to track all member products (think Etsy type of marketplace ecommerce site) on a shopping category grid view page.

This page will show many products that belong to many unique sellers (members).

is it possible to have an array of values in the page vlaue slot?

eg
piwikTracker.setCustomVariable (1, ‘Member’, ‘<?php echo $all_member_ids_as_an_array ?>’, ‘page’);

…so that we can track the number or times each user has their products shown?

…also, are the 5 custom variable slots a per website thing or a per database thing?

eg, if i am tracking 10 different websites, can i create 5 unique slots for each site? Each with numbers 1 ~ 5 ?

Or do I need to reuse the same 5 slots with the same ids?

You can track the same “Custom var name” in different slots ,so you can track up to 5 values for each custom variable.

Hmmm, that’s pretty limiting. There could be 50 sellers on the page, and we want to track impressions for each of them.

How would you recommend tracking somethign like this Matt?