Yeah I figured this one out using AppleScript. The workflow opens the Freedom dashboard, clicks on the blocklist and device you've asked for, and then starts the block.
Notes
I have an external trigger in there so I can link to this workflow from other workflows. It's not necessary; you can get rid of it.
"Whitelist" means block all sites and "blocklist" means block the first custom blocklist you have. You'll have to customize the AppleScript if you want to change what lists the workflow clicks on.
The workflow very very rarely doesn't work: you select a block, it open the dashboard and tries to start it, but something messes up. I think this has something to do with the webpage not loading properly or looking different from what the AppleScript expects. It'll work when you try it again. It never fails multiple times in succession.
http://www.packal.org/workflow/freedom
