Are both inventories supposed to be visible at the same time or can only one be seen at time?
If the answer is the latter then you could setup 2 additional characters & use one for the main inventory & the other for whatever the other inventory is supposed to be & add the relevant items to each of those characters instead of adding them to the main character, because you can just update the main characters inventory to be the same as either of the two mule characters inventories with a single line of code just before you show the inventory that you want to open. Here's the line of code... (use in an execute a script action part)
game.CurrentCharacter.Items = Characters["Tom"].Items
& that's it. Pretty simple no?