A counterweight won't make life much easier because you need to lift it and put the same amount of work in (or more) as lifting the original load. That 90 degree 'lever' arrangement can't help much because, when filled up with the rocks, the centre of mass needs to be lifted higher than necessary and that involves mechanical work each time. A flat plate or shallow tray / sled, dragged over a smooth surface (rails) is the easiest to implement. Wheels would need to be small diameter if you don't want to be lifting any distance. Any lifting should be done on small parts (man manageable - say 25kg) of the load. Trying to do it all at once is likely to be counter productive.A big 115 degree U shape with counter weight can move the rocks fairly quickly for short distances up to 5-6ft
Anyway, there is no quick fix available from 'Physics' here.
I really wonder whether this thread is near enough to April 1st to be a bit suspect. I could recommend trying telekinesis.