Pictures would help,but we must be dealing with some extremely soft rock! A lot would depend upon one's rock climbing/scrambling ability, but at 5.5' height a mantle move might be just the trick. If the rock is really that soft, almost anything, like a tin cup or even bare hands (used judiciously) would provide suitable indents....but that would be cheating. And I thought the Channel Islands had soft, crummy rock!

A trail of use,such as you describe, is not what comes to mind for the phrase "well established trail." It suggests something that is constructed.