Ive added Multi Account viewing for this addon. Ive tried contacting the original author (TheGooch) but it seems hes not been active in curse for a long while. Ive placed a download link in the comments of the addons page and ive placed both links below.

Inventory Viewer on Curse

My Inventory Viewer version download

Features-

Upto 10 accounts can be viewed.

Left/Right buttons to flip through the different accounts.