It is now possible to print single sided by redirecting the job to a
-simplex queue. This is done by adding "-P<printer>-simplex" to the lpr
command.  Example: This would print single sided to gutenberg:

echo hello | lpr -Pgutenberg-simplex.

There are -simplex queues for most of the printers around the department,
a notable exception is the HP4Si in the main office which does not have a
duplexing unit.