After much searching and experimentation, I have found out how to print to the Aficio using double-sided printing. It turns out that there is a printer driver that will work for any PCL printer. To get your PCL printer working, just install the high-quality HP 'hpijs' driver. You also need to install Ghostscript if it's not already on your system. Easy-to-use install packages can be found on this page.
Then just set up a new IP printer in Print Centre. Enter the printer's IP address. For the model, choose "Generic PCL" and select the PCL model name relevant for the version of PCL your printer supports (PCL 5e or 6 for the Aficio 2035e).