Get a tap, re-tap the drain hole and you can put in the appropriate sized drain plug for the new tapped hole. Autozone can talk you through it if you aren't sure how to do it.
yea thats gonna be the best bet unless you wanna be cheapo and put some silicone on the drain plug and put it in and it will seal it.thats what i did on my car and it works fine but i suggest just tapping it