Not possible. I sent them an email and that was the response I got (not even possible in Foursquare app). It must be done via website in browser.Through swarm not foursquare
I cannot even get the Foursquare app to install since it updated. It throws an error about my network, even though my network is fine.It's possible. I've added two venues in the last week, from my phone. You add it in Foursquare, then in Swarm you have to search for it.
You can also create a place on your phone by going to leave a tip, searching for the place (this step is important!), and then if you can't find it, scroll down to the bottom of the list and click "Add this place?"