I'm assuming that you don't have a commercial trailer that has a deck that is high up off the ground. If so, you are only rolling it up a mild grade. You won't be lifting it vertically so this isn't going to damage anything. If pulling on the forks concerns you, there is a loop on the left-hand side tip-over bar that is easily accessible without having to remove the cover. You don't need to pull from both sides of the bike, the forces aren't great enough to be a problem. Hook on to that loop and winch away. I did it once winching an ST1300 up on to a landscaping trailer. I thought that winching only on the one side might make it hard to keep the motorcycle stable but the force is being applied so low down that it wasn't a problem.
Having said all of that, there is another option that you might want consider. Light-weight aluminum ramps can be had really cheaply now. If you don't have enough width on your existing ramp(s) to walk up on to the trailer beside the motorcycle while propelling it up the ramp using its own power, buy another ramp section so that you can do so. Much easier than winching, much safer for you, and much easier to stabilize the motorcycle on the way up.
