I've attempted to remove a similar freewheel with a file clamped in a vice. The net result was a broken file. I would recomend taking the wheel to the lbs because it should cost about $5 and 5 minutes to remove the freewheel. If that's not an option, then purchase or borrow the correct tool for removal. If you absolutely can't do either of the above, I have removed similar freewheels with the very careful use of a hammer and punch in the slot to turn it counterclockwise.