Ok you could build in a clause for Bezerkers, call one last flaming frenzy.
But I still think that a huge funeral/wickerman/bonfire is a fatality and not something that a normal Gladiator would jump through and continue fighting with a slight smell of burnt hair about them.
Because even in those days fire and water were the two biggest fears to a mortal man. The risk of infection and death was so high that even a minor burn could be a life threatening.
If you do want to try that you could add the tactic I'm planning on using for Trap doors over Pits which would be to roll a die and on 1 or 6 (or odds vs evens if you want less fatalities) the Gladiator moves over the terrain and lands on the other side. In the case of fire I would also remove a couple of points Vitality as leaping through flame would definitely singe your Vitals.
EDIT: I've opened a thread in the Rules\Suggestion and Discussion on Addirtional Terrain Rules to prevent hijacking this arena thread.