Draw a construction line diagonally across the sheetmetal face that you want the explode trail centered on. Then draw a line from the midpoint of that construction line perpendicular to the face.
I've had to do it like that for the last 15 years.
It also wouldn't hurt to file an enhancement request to facilitate creation of an explode line from the centroid of a face or body.
My worse nightmare has been confirmed!
I was use to Inventor where you can't make the super customizable 3D line BUT it automatically generated the explode line using the Centroid. Honestly, hardly ever needed anything so customizable, it was so fast. Anyway, thanks again!
(For straight lines only), you can create sketches or axes inside your hardware, then show them on your drawing.