The best way to do this would be to set up a state machine which determines when the cursor is over the graph. When it is, you make the controls visible. Otherwise, they are invisible. Now, how you create the state machine depends upon which version of LabVIEW you have and how you prefer to build this. There is a great tutorial on NI's website which discusses state machines. You may want to take a look at that if you have not built many of them.
J.R. Allen