Pour sodium chlorate (weedkiller ) onto the stump and add a bit of fuel.
Sodium Chlorate is an oxidiser and should help the fire along quite a bit.
Don't burn your eyebrows off though!

Andy.

Sodium Chlorate weed killer is now sold with inhibitors to prevent it
being used as a oxidiser, ie for rocket fuel or explosives.
I don't know how effective it is though, you may need to get it really
hot in order to get to release its oxygen.


Cheers

Dave