I did something very similar with my motorcycle and drain bolt for the oil pan. Here are some tips that might help you get it out.

First thing is don't try to force it out, it will only strip the bolt further and make it harder. You need to ease it out. I am guessing the bolt is made of some soft aluminum and is just stuck. Spray the heck out of it with some PB Blaster or something similar. Get a hex nut that is one size larger than the 10mm. Don't use a hex key, use an actual hex drive with a socket, works way better. I used a hammer and had to "punch" the larger hex socket in using a hammer. It wedged itself nicely and I was able to break it free that way. It wedged itself in so nicely that I couldn't get the hex socket out after wards. Small price to pay to get to removed.

Remember, once you have that socket wedged in there to ease it free. Don't pound or force it to much. If that method doesn't work get a 10mm socket and JB Weld or weld the socket in there.

Both methods cost you a socket but better than having a stripped drain plug.