I should be possible to do with SP, the same way you do with MP.
I'm not entirely certain of the syntax here, so someone can correct me where I'm wrong.
Bring down the console, type "devmap XXX" where XXX is the name of the map (view the readme.txt file that was shipped with your game for a listing of default map names).
I believe then, you type "thedestroyer", without quotes to enable the blade.
Go back to the game, turn on your lightsaber, and see if it worked.
Like I said, I have never done this, and am writting this my memory.
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