Doesn't look like this'll be an easy one then, you reckon?
I think so. Sounds pretty difficult.
Perhaps global variables and the mouse move event to keep track of where the mouse cursor is. You'll also need to leave some form space both above and below the controls because if you're moving the mouse from control to control the mouse move event will never trigger.
The record set will also need to be sorted and ranked so it can lookup the correct record depending on the Y coordinate.
Edit: This will be impossible if there's a scrollbar, because even though you scroll down, the actual coordinates don't change at all. So unless there are only a few records, it's not going to work.