Show <string>List from storage in subtitle?

I'm trying to make an inventory system that will utilize a list of strings (stored in storage) to determine which type of item is in which inventory spot.
I would like to have constant visual feedback on what is in this storage data, via the subtitle (since I can't put strings in scoreboard values), but I'm not sure how to do so.
I need something like...
title @p subtitle (data get storage sbm1:storage inv_items)