Printopia is a great tool for exposing non-Air Print printers on a local network so that you can print to them from any iOS device. But even better is that it can expose PDF Workflow to do your bidding. In my case, I wanted to do n-up printing (n pages per sheet).

To do this, open up Automator and create a Print Plugin. For the workflow, you only need to add a single Run Shell Script action with the following line:

lp -d -o number-up=2 -o media=Letter “$*”

The details of the command will vary depending on your needs. In my case, I wanted 2-up printing to go do my default printer, so I could exclude the -d option.

To see a list of available print queues, type lpstat -a in terminal.

Once you save your Print Plugin, go to the Printopia in System Preferences and add your new plugin as an available destination for printing.
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Source: Mac OSX Hints