Publishing a single-author paper
My best guess is that you are well and truly stuck. There may even be contractual considerations that prevent your desired action. Some places (though mostly in industry) claim that anything you produce, even on your "own time" belongs to the institution. You can look to see what binds you legally. 

I also don't know your field and won't judge whether a paper without your supervisor would be looked at a strange or normal - especially if he objects. That expectation varies widely by field. 

But my advice would be to do what ever you can to find a different, and better, situation. Run, don't walk, to the nearest exit. If this means bowing and scraping to the chief to get a good letter of recommendation, then go along for now. 

I don't know how hard it will be to move with few/no publications. But it is usually pretty hard to go without good letters. If you can use him to get a better position you will have a chance for a career.