'07 BMW G650 XCountry

Mod: Install KTM Axle Cap Nuts that use common 27mm wrenches, and also stainless wheel spacers

Then I discovered by reading AdvRider that you can buy KTM axle nuts that use a 27mm wrench, and have the same pitch so they fit.
I bought 2 KTM rear axle nuts, part no. 50310099000 (from an '07 KTM EXC 450, for example), for use on the front and rear axles and they fit with a slight mod to the rear.
Note the new nut is aluminum (not steel like the BMW) and is a cap so the axle threads are completely hidden. This means if you lay down the bike on some boulders at 20mph, you won't bugger up the axle threads like the OEM nuts would have allowed.

Only one modification is necessary (On my '07 Xcountry at least):
The front just fits fine, but on the rear axle the diameter of the flange on the KTM nut is bigger than the BMW nut and won't fit inside the chain adjuster block. It is not obvious and I think many guys missed this by saying "they just fit" but it is not safe IMO. There is a single washer under the nut so I think the easy fix is to add another washer, or what I did is had a small machine shop chuck it in a lathe and easily turn it down a bit to fit inside the adjuster block.
In these pics you can see that one nut has a smaller flange diameter and this one is for the rear.

Then tools:
Now this lets you look for a 27mm tire wrench. Here's a few choices:

• On the cheap end, there is a $3 steel Honda Eye Wrench (27MM) 99006-27000.
  
• On the exotic end there is the aluminum Motion Pro T-6 Combo Lever 27mm for $30,
  
• ...or for lightening your pack, add on a 3/8" drive adapter that turns it into a 3/8 socket drive, as reviewed here and honored here.

I'm thinking that the cheap Honda steel tool would work fine if it was a steel nut but might be a bit thin for the aluminum nut and the Motion Pro might be the way to go.

Mod: Scheffelmeier Stainless Wheel Spacers