I just have to plug this - the "How Publishing Really Works" site led me to it, but it strikes me as a terrific idea.
I type slowly enough that my creative juice has become able to cope with occasional halts for spelling corrections and so forth; they don't really break the flow as it is so sluggish to begin with! But as for those tense moments when what stops me is some infelicity of phrasing, some paragraph that doesn't quite sound right - for those nerve-grating times I think this could be a trick worth trying. It's rather like the "Just write something" idea, but more subtle.
Letting the inner editor, as Andy Shack calls it, step up is not just a problem, for me; I think it is also a tacit procrastination tactic. If every time I am working on something, whether it be writing, drawing, painting or what, I let this inner nag lean over my shoulder whispering "That isn't much cop, you'd better fix it or there's not much point in going on", then I am setting myself up to stop and drop everything. And that is simply stupid.
So I will be trying the "hash key" technique; and if I start doing any more developed painting or drawing, I'll be looking for a visual equivalent, too.