If you want to do this just once, you could open a coronal image viewer on that dataset, open the Disp control panel, and turn off all the 'Save to' options, and turn off 'Save One'. At that point, the 'Save' button in the image viewer should now show 'Save:bkg'. You can now use that button to write the image sequence out.
If you want to do this from a script, you can investigate the from3d program. However, that program is highly limited in what it can write out, and you might need to flip the 3D orientation of the volume with 3daxialize first, before using from3d.