I would only tow it that far on a dolly, or flatbed. Even cars being towed relatively short distances shouldn't be towed with the drive wheels down, this is according to every tow truck driver that comes to the shop.
Here's a few tips to get you back safe:
1) For a RWD Mercedes, rear wheels must be on the dolly, car towed backwards. Otherwise you WILL damage the transmission.
2) DON'T use the key to lock the steering wheel straight, that's suicide. Keep the key in the ignition and turn it one click so that the wheel is NOT LOCKED, but the ignition is still OFF. Leave it that way for the entire trip.
3) Take a good piece of rope and tie it around the spokes of steering wheel, (not on the upper rounds where it can possibly slip around and loosen up on you). Do this on both sides and leave enough rope to go through the door and over the roof. This is your primary tie down, you can use the upper rounds of the steering wheel at 10 and 2 O'Clock -afterwards- for a redundant tie down point. (highly recommended)
4) Make sure the wheels are dead straight. Open the drivers door, pull the drivers side rope tight -and up- then slam the door shut while holding rope. The rope should be caught between the top of the door frame and the roof. Do the same on the passenger side. Make sure wheels are still straight and tie the two ropes together -securely- on the roof.
From the steering wheel I usually go to several places on the car to secure it even further.
Before you slam the primary ropes in the door frame, tie a second set of ropes to the wheel at 10 and 2 O'Clock to be used afterwards for redundancy in case a primary rope breaks or loosens up.
Secure second ropes to any of these places:
A) Arm rest/pull handle in door
B) Hold down handles above door
C) Headrest post
D) Seat frame, or any secure point that you can find.
That should do it, you already know to drive conservatively so I won't go there.
Good luck bro!