what you need are three things (you could get away with just 2)

A large cardboard box.
A tumble dryer vent tube: http://www.amazon.com/Deflecto-Conne...ryer+vent+tube
small fan (optional)

make sure the cardboard box fits over your printer and the printer can still function.
Make hole in top of box so that the tumble dryer tube is a nice tight fit - ducttape might help.
put other end of tube out of window.

Job done.
As the printer warms up the air will rise and go through the tube, it will create an active draw.
You could use the fan to help it, but once you've got warm air in the box and cold air out the window, it'll naturally create a draw.

You might want to cut a panel or two in the box and cover with clear plastic of some kind so you can see what's going on. Empty laminate pouches are ideal for this. Or any thickness perspex. Large clear food bags work as well.

Oh yeah:
At the moment I only print with PLA as it is the only material known to be safe without venting.
Afraid not. It still produces micro particles that might or might not be hazardous to your health. Just because it doesn't smell horrible, doesn't mean it's actually good for you.