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An alternate method requires that you have a switch (item 7 in thumbnail above) that has already been removed from another car, or obtained online. The harness connector can then be pulled off the switch that is in your car (remove instrument cluster for access), and connected to the separate switch, which can be operated with a screwdriver, as noted by D911 above.
Here is the lowest priced one on ebay:
https://www.ebay.com/itm/Ignition-Starter-Switch-Mercedes-1977-2004-2025450104-New/292344116030?fits=Year%3A1985%7CMake%3AMercedes-Benz&hash=item441111333e:g5cAAOSwcBhWXy4e