Combine gym time with stump removal. Assuming it's cut close to the ground, grab an axe and take some swings each time you go outside. It won't take too long to be reduced to chips.
Fwiw, I try not to use chainsaws for this as the dirt is so bad for them. Pruning blade on a recip saw makes quick work of roots. Make a cut close to the trunk and another one out about a foot gives you a path to dig. Get a path under the stump and slide in a jack. Pressure plus cutting other roots has it come up. You're left with an huge dirty chunk of wood and a big hole if you choose to remove it this way.