An app for IFC is now available. Comcast isn't officially supported but you can hack your login in the same manner you can with the AMC app (and many other channels not supported by Xfinity). Use this url and replace the ***** with the activation code:
https://api.auth.adobe.com/api/v1/a...rl=http://www.ifc.com/activate?device=appletv
https://api.auth.adobe.com/api/v1/a...rl=http://www.ifc.com/activate?device=appletv