Duplex printing with HP DeskJet 6122

[Sheldon Hearn]

Hi folks,

We just got an HP DeskJet 6122 for printing Unix docs.  It comes with a
duplexing unit, which works when driven by the supplied Windows driver.

However, I'd really rather have this thing connected to my FreeBSD
workstation.

I've tried CUPS and LPRng, and neither of the two support this printer's
duplexing feature out of the box.

Does anyone have any suggestions?

Ciao,
Sheldon.