Have an open saved game slot. Also backup your current saved game to recover in the event of an error. Go to the Einherjar Shop and purchase any desired unit(s). Save the game into the open saved game slot. Hold L + R and press Start to restart your system. Reload your original saved game file. Delete the file that was created in the open saved game slot. You will retain unit(s) that were purchased in your Unit Logbook and no gold was spent on them. You can also use this trick sell items from your inventory to gain more gold to more purchase more expensive units.