get a few 30 packs, a dozen friends, some shovels and let them have at it!
Really though, i would dig around the tree and get as many roots as possible. You wont be able to get them all the more you can get the better!
put your strap or chain on it and try to pull on the far side OVER the stump.. Have a buddy throw some stuff under the stump so it wont fall back down.
Dig more around it and keep doing this ....
should be able to get most of the roots and you can tug on the strap a little and probably be able to get it out. If all else fails, call someome with a bigger vehicle!