This site simply states “I rode him like a Russian Racehorse”
http://www.sanitycentral.com/lonelyhearts/17lonelyhearts.htm
From some online fiction at the site… http://www.win.bright.net/~haukepub/mike.htm
“He grinned to himself once again thinking about the popular Roman expression: Gotta piddle like a Russian racehorse.”
Tarnation, I’m punching holes in my own theory.