Can a tarp withstand the heat currently generated? I suppose any material with high heat resistance, low weight, and not too gas permeable would do. Snuff the fire (once capped, it should naturally burn out from a lack of available oxygen), pump and productively burn the gas.

Since this comment chain was about the worry of methane release after stopping the fire, I'm assuming the fire would already be put out if necessary.

Perhaps there is a nearby source of sand.