Paul,
Heed Chris's warning, but if you are going to try, start with a cold, plain water extraction.
Since a cocktail of chemicals has already been added to the coffee you must not add further without this innitial flush.
Next I would try something like B144 Stainpro before moving on to reducing agents. Flush out again.
Prochem Coffee Stain Remover would be the next step, and the last resort would be one of the sodium metabisulphite- based products.
Having said this, the chances of sucess have been reduced first by the fact that the full pot of coffe was undoubtably very hot and the quantity would mean that the heat was retained for some time. The likelihood that the dye-sites of the fibres have been opened to permit ingress of the coffee pigments is high.
Secondly, the DIY disaster would, in itself, likely have set the stain permanently.
John.