Steam effect

hey,
I’m shooting a really short movie, and one shot needs to convey the message that it’s really cold. Basically the char opens a box and ideally i want his breath to fog up like when it’s really cold… any ideas on an easy way to do this? Its not actually going to BE cold, so he can’t just breathe normally… the only thought i’ve had is to try and incorporate steam somehow but i think it’d be tricky, and lame.

oh and btw, aftereffects or similar programs is out of the question, we’re not allowed to use it.

suggestions?