Saw one pulled out today, didn't see the exact setup as I was digging my sled out, but it looked like they had a rope from the back of a sled to the frame if the bike.
We've had good luck doing it. I've been towed and been the one towing. We usually tie a strap to the bike frame behind the number plate, in-between fork tubes. With the strap there you can still steer, lean, etc. Just put the bike in neutral and tell the tow vehicle to go.
It seems crazy, but it is not obvious for the guy on the tow vehicle to tell if the guy being towed has fallen over if your on a groomed trail so the guy towing needs to be watching.
Also, the bike feels different when being towed. The hardest part is getting moving, and once you to its a lot easier to stay upright but a fall or two when just starting to move is not uncommon. 15 to 20 miles an hour feels ideal.
Things that haven't worked well:
Tying the tow rope to the ski
Tying the tow rope to the forks
Climbing in deep fresh snow while towing
Towing someone who thinks you can hear anything they are screaming at the top of their lungs whilst being towed.
Being towed by someone unsympathetic to what your trying to do while being towed.
fair trail in new deep fluff,a bike had engine issues this am, towed 6 miles back to truck on wide packed trail, with 12 ft of pull tape, I followed, they went along about 30mp, I had to be in 5 or 6th just kind of lazy motoring but we moved right along. Had to pull the radiator cover on the 450 ktm pulling, but otherwise not too bad.
Had a fairly long tow out last year. After a few failed attempts and laughing we found the best solution was this:
take a long strap (preferably 1" wide webbing) and wrap it around the handle bar in the center 2-3 times. Leave a tail long enough to reach the left grip. This was of things are going south you can let go of the tail and the strap will unravel and you won't get drug behind the tow sled.
^ This is similar to the method we use, except we wrap it around the Timbersled spindle cross brace (the one the rear bolts thread in to) a couple times, then up to the handle bar grip. Wrap it a couple times and you can hold it with your hand pretty easily.
If you're heading towards definite disaster, just release your hand and the strap is released.
Towing from down low near the ski helps the towing bike too, because the track on the towing bike isn't being lifted as much.
Whatever the method is, its a difficult process. Riding the towing bike is probably more challenging than being towed honestly.