Personally if I figured out a way of firmly attaching an infant car seat to a two wheel trailer I would do it, but that’s just me and I’m a bit nuts. I also seem to recall seeing an infant car seat between the pilot and stoker on a tandem (or was it a triple) that looked like a nice setup allowing stoker to also calm the baby while riding.
I did find a couple of links that you might be interested in
http://www.biketraffic.org/content.php?id=27_0_6_0
http://www.ibike.org/education/infant.htm