Didn't realise there was a reply to my question.
This doesn't exactly work as expected. If I open the tooltip as a modal, and the data changes after opening. expanding the height/width of the popup, just setting the x/y cords doesn't help position the modal in the correct place.
To recenter it I ended up using jQuery to get the Height/Width of the wrapper.
Set the top/left position to 50%.
Set the margin-top/margin-left to negative half the height/width of the wrapper.
This re-centers the popup correctly. This feature should be built in by default tho. I should be able to call tooltop.recenter(); and it does this for me.