To create mid-span poles, select the Pole tool on the toolbar:

and click on the conductor, to place the mid-span pole. You can use the Precision Placement tool to edit its exact location.

All conductors spans that are equal to or lower than the above ground height of the mid span pole will automatically be attached to the mid-span pole.

To place mid-span poles to attach to lower conductors only, choose a suitably short mid-span pole.