Writefreely spam account minimisation?

is there some way to minimize spam signups besides making the instance invite only and thus a bit labour intensive and not as friendly ?

i figure, someone somewhere is getting some use of doing this, or they wouldnt be making these pages for their business, like this - so for now im not bothered by it, as its only a dozen ish of these.

it would be nice if they actually, blogged, though.