This has been my experience as well - the content of the ToolTip is set via functions and only the information about the content being expressed by the ToolTip is updated. Unless I am mistaken, there is not *always* a reference back to what content was used to generate the ToolTip. With PopupTooltip for linked items, the item information is saved in a variable local to the ToolTip control called .lastLink. Otherwise, I have not seen anything.
So yes, what you mentioned should work great for generating a ToolTip from scratch when you know what you want to show.
Let me know how it goes and if you find out anything else on this topic as I am quite interested with my current development.