I also launch solo a lot and I do the long line tied to the front cleat, back in till the boat is floating, pull the trailer up so I can grab the rope, pull boat to dock and tie off, park truck, then get to boat, start engine then leave the dock. A few places I fish have long docks that when I tie the boat off I pull the boat as far back as I can then someone else can launch their boat. I know of no other way when your alone how to do it.
Many times I can launch faster than people with two or more people. If someone is having issues or newby I just tell them to take their time if there is not a huge line. If they get frustrated it will then take a lot longer to launch or retrieve. If they are moving just slowly I have more patients than the people who load or unload on the ramp.