Following on from How can I upload screenshots from my Wii U? I'd like to know how to take a screenshot of my Mii.

I'm growing a moustache for Movember and I've just added a moustache to my Mii to reflect my current appearance. I want to take a screenshot of my Mii and post it to Facebook.

The screenshot feature doesn't work from all software titles and I haven't found one that will work yet. So far I have tried from the home screen, the Mii editor in User settings and in Wii Fit U. Every time I try it I get a message saying "No uploadable images."