Based on what you can find here: 

https://docs.servicenow.com/bundle/newyork-it-service-management/page/product/service-catalog-manage...

• A multi-row variable set is supported in the variable summarizer only in Service Portal.
• You cannot set Global as True for any variable that belongs to a multi-row variable set. So, a multi-row variable set is not available in catalog tasks.

I don't believe you'll find a precise solution for this, as for all intents and purposes, this is behavior as designed. 

I did however find this article: https://community.servicenow.com/community?id=community_article&sys_id=c70c9e3adbeb6f001089e15b8a961...

This provides some insight into how to format an email or a description field with the values, which you might be able to adapt to your purposes.

I hope this helps!

If this was helpful or correct, please be kind and remember to click appropriately!

Michael Jones - Proud member of the CloudPires team!