I've loaded plenty of big heavy bikes by using two ramps... one to walk up on beside the idling bike, with the bike on the other ramp, slipping the clutch and giving it a little gas under it's own power.
Just take it slow and easy and keep two fingers on the front brake lever... if you get squirrelly just pull in the clutch and grab some front brake to keep it from rolling back while you get re-adjusted... a little at a time.
To unload, use the same two-ramp method, only the bike doesn't need to be running. Just use the front brake to control how fast you want to let it roll down the ramp as you walk down beside it on the other ramp.