I have introduces a Edit -> Set Origin in the Nightly's that I post. But this requires your action, it is not completely automatized like you suggest. You have to click where you want the origin to be. In FlatCAM 8.5 or the master branch of FlatCAM, there are only the offset possibilities where you have to enter the offset value by hand.
But I see that @idechix is doing exactly what you want here: https://bitbucket.org/jpcgt/flatcam/pull-requests/79/adding-gui-interface-for-mirror-and-auto/diff