It should be possible to dynamically pop up specific text in your
tooltip. I did this in a small map control i did. Basically i hooked
into the mouse move event for the control you are interested in. In the
event handler i looked to see if the tooltip was active. If active i
then analyzed where the mouse was in the control. I was able then to get
the specific information about the item that was under the mouse. You
can then set the text in the tooltip and display it. Following is the
code where i set the contents of the tool tip. It is taken out of
context but hopefully gives you the idea.
ToolTip    tt = mapControl.toolTip1;
RectangleF rec = new RectangleF(x - 2,y - 2,4,4);
PointF     pt = MapToScreen(mob.x,mob.y);
if (rec.Contains(pt))
{
    tt.SetToolTip(mapControl, mob.TargetInfo());
    tt.AutomaticDelay = 0;
    tt.Active = true;
}

TargetInfo can create a pretty complex set of text. It uses a
StringBuilder to do that and you can use multiple lines of text by
Appending  \n characters.

Hope this helps
Leon Lambert