Ways to attract butterflies

[Michael Healy]

I recently  observed a few P napi mud-puddling in much the same place as
last year.  In this connection, a friend from Malaysia tells me of
observing a row of Chinese butterfly-collectors, early in the morning,
solemnly urinating onto a sandbank so that butterflies would come to the
salts left behind after evaporation.  
Apparently the manoeuvre was very successful.  Has anyone tried it in a
temperate climate situation?
Michael Healy