I'm not sure you can - their design is forced air into a flame into a dome end. Not sure HOW you could vent it... there is no "heat exchanger" in these, it's the actual flame doing the heating of the air. I run one of these, outside the door of my shop, and while it works well, you DO have to keep the door open as it WILL asphyxiate you.
If you want a vented heater, I'd go with the old school ceiling heaters like they have in older industrial settings. They work well, and a plus is you thermostat them so you can keep your shop from freezing (one of the issues I have every winter). Kind of what I'm looking at now, once I get the space to install it. You can usually get them 3rd hand at municipal auctions, find them on Craigs or eBay, etc... even new online.