Reverse Tether - Share OSX Yosemite Wifi Connection Over Bluetooth
In order to do this in Yosemite, you'll need to go back to the main screen of System Preferences and click on the Sharing preference pane. In the sidebar, there will be an Internet Sharing option. Click on this to view its settings.

Now set the "Share your connection from" drop down to Wi-Fi and then check the Bluetooth PAN checkbox in the menu below. Next just make sure to check the box next Internet Sharing in the sidebar.

Once this is done your Mac should be sharing its Wi-Fi connection to devices in your Bluetooth PAN.