I have that problem on the GZ, but more so on the Ninja. I compensate on the GZ by actually pulling the mirror "into" me a little more and using the outside edge to focus directly behind me. It's not bad, and I only have to pull my elbow a tiny bit to see directly behind. Then Ninja is hopeless though. I'm always having to tuck my arm deep in to see back.
I figured it wouldn't be so bad if my arms weren't so ripped and I wasn't so damned buff. I guess you take the bad with the good though.
