Hi
We had been cleaning cinema chain seats for months and I have been looking for efficient and effective way of doing it for a long time (money in this is tight) - you might be lucky to have a client that is prepared to pay reasonably though.
Its not an easy job and I need to say I hated it. Time pressure is incredible. The seats must be dry the following morning. Method choice the night you clean them is incredibly important. Again, you might be lucky to do them in parts or have more time than couple of hours to dry them.
Probably environment with your clean would be similar to the cinemas we have cleaned i think.
Its not ideal but the way we found most efficient way on relatively fresh chairs was to go round and apply citrus gel on chewing gums, prespray then back and start again with portable extraction machines (easier to go in rows - problem with frequent refilling of the tank though). Gums scrapped with stiff kitchen knives if needed.
Good looking seats - Minitex from tehatherm or alike machine - orbot mini or even a good drill tool with flat velcro pad that you can attach a pad to. Minitex is good due to a long cord but the weight can be felt on shoulders after 6 or 7 hours shift.
Encap and agitate. Want to, you can rinse with portable.
If you can move the chairs in your scenario then I would not use anything else than this:
http://www.santoemma.com/default.php?t=ecomm&eid=00015&vimgd=&el1=100&el2=10030Hope this helps