none of us MB Diesel owners EVER make this mistake... Um you belive me right?
anyway, usually the help is posted similar to what you posted. like "help I put in the wrong fuel" or "HELP QUICKLY" or something similar...
anyway, yeah, siphon out as much as possible, put in the 5 Gallons you have into the tank, it is probably best to remove the fuel filters empty them, fill the spin on with diesel, or tranny fluid, siphon out a quart of gas from the supply line ( the one hooked to the clear in line filter) and crank it until it runs smooth. then go fill up.
it would be best if you had 10 gallons of diesel to put into the tank, for two reasons, first the gas will set tons of gunk free from the bottom of your tank, and the second is you can't get all the gas out, so mixing with as much diesel as possible would be best.
John