Welcome atemme,
I don't have an example, but it sounds like you're off to a great start. What you want to do is place a waveport (in a driven modal simulation) on the edge of your air box that covers both of the wires' ends. To ensure that you are exciting the correct mode, draw an integration line between the two lines.
Be sure to look at the fields and check which mode is being excited. If the distance between the wires is large, HFSS may initially pick the incorrect modes. If this is the case, you can simply increase the number of modes that HFSS is solving for, and it should eventually get the correct one.