Rotating /sliding your handlebars back and forth are a good start. I notice that your bike seems to have standard BMW grips. These are usually pretty good for a number of riders, though some find that either larger, or smaller, or more cushioned grips help,d epending on if it is the diameter of the grip/size of their hand that comes into play, or just vibration. Where on your arms do you start to experience the numbness - up at the shoulder, around the elbow, or wrist,

Sometimes numbness can indeed be from putting too much weight on your hands - though this usually ends up causing numbness in hands first. You are doing the right thing by analyzing your posture/stance - with a 'naked' bike you should be just slightly leaning forward to better deal with the wind at speed, but not so much that you are putting alot of your upper body weight against. your hands. You also shouldn't have your elbows pointed way out to the sides, as this tends to exacerbate that problem. IF you can get into a posture that is best described as sort of like "sit up and beg", with elbows closer to the body, slight lean forward (but not much) at the waist, you may find it to be more comfortable. IF those bars don't enable you to achieve this posture with rotating them front/back you might want to look at some bars with different width, rise, and pullback. They also sell a brand of barbacks that fit the R65 top fork yoke, but I cannot recall the name at the moment.