An interesting topic and I'm surprised it has never come up before...or has it?
On my M, my inflatable, the 'Flubber' has quite a long painter, I suppose it must be 9' or so, and as my boat is on a swinging mooring in the middle of a river, I always have to board from the water, so I come alongside the side of the cockpit, and pass the dinghy painter around the middle stanchion, then back around the cleat, then around a loop of rope on the dinghy engine and back to the cleat where I make it fast. I then undo the lifeline, step onto the side tube and just flop over the bimini frame [it's folded], not elegant but easy. I've even got my wife doing this with not too many complaints. There was a bit of muttering about it being 'not easy' so I made a rope ladder over the winter, but haven't actually used it yet as she has adapted to 'not easy and inelegant' quite well. As has been previously mentioned the trick is to secure the flubber tightly to the boat so there is no movement.
When I am towing, I just tie off on the rear stanchion and take the balance of the painter line around the cleat or one of the forward stanchions. Even with the motor on she seems to tow quite well, on the river at least, it may be another matter in a following sea
Paul