Hi there!
Currently, it is only possible to pivot query results which return 2 dimensions and 1 metric, according to docs. Okay. My suggestion is, when I have more than 1 metric, but hide all, leaving only one, I should be able (I think, at least) to pivot it as well, since I'm only seeing 1 metric.
Currently, that is not possible:
I'm pretty sure this is not as simple as it looks, since it would change underlying data reading, and something (not to mention that, probably, the "hide column" feature is most likely visual, from where I stand, not affecting the actual data object). But, here is the suggestion.