So first we made sure the sticks were level enough to stand up, knowing they did not need to be perfect. Then the DH began to drill two holes in the stump. A paddle bit would have been easier but he made do with large boring bit.
Because of the guesswork involved with the drilling, we had some large gaps to deal with.
We decided to pour in a small amount of wood glue, fill the gaps with the readily available sawdust, then pour glue on top and press the mixture in.
It was messy, but it worked surprisingly well. By the time we were finished all the drill holes were nicely concealed and we were able to sand things fairly smooth again. It did also serve to make sticks very securely fastened to the stump.
Next time: the treehouse.