I think USB-to-parallel is standardized, all of the BSD's have a
ulpt(4) driver.
QEMU has the -parallel option, so the command on FreeBSD might be:
% qemu (options) -parallel /dev/{ulpt0 or unlpt0}
I'm not sure which one you must use, but you'll need to make sure you have the correct permissions to access that device node.
I hope this helps