Thanks all for the nice feedback.
As far as drilling a hole or holes in the base of the key - yes, I think that would be a good idea. I did drill a hole in the keys when I made the knobs for my 2001. I should have put a hole in the ones for my 2010, but I got a little lazy and neglected to do that. I don't think it will matter, but it can't hurt anything to drill a hole.
One thing that I failed to mention that should be brought up:
These knobs could be a security issue.
I use my wing for commuting and day trips and never leave it overnight anywhere other than in my locked and alarmed garage. So I have never really given much thought to the security aspect. If I were to leave it outside overnight, I would definitely take the knobs out, however.
I have not tried using the knob in the ignition (I don't want to risk breaking one of the knobs), but there are other posts that say they are not long enough to turn the ignition on. That said, though, if someone were to swipe one of the knobs they could get a full #27 blank cut and have full access to your machine.
In most situations, I doubt that anyone would know those were keys - they obviously look just like the radio knobs. However, it just takes one creep to ruin the comfort of that idea.
Someone posted on another board that swapping the lock cylinders for the fuel door and right pocket with a GL1800 friend would be a good idea. Sounds good, but then you have the security issue that each of you has the other's ignition key.
So, other than taking the knobs out each time you park the bike, I don't think there is a way to keep them from being somewhat of a security issue.
I guess it might be possible to get the cylinders re-keyed to not match the ignition key. But, if you were to go to that extent, you might as well gut the cylinders and make them work with a plain, uncut key blank epoxied to radio knobs.