I wrote an app for the FitBit Versa and Ionic which will start/stop climate control on the Nissan Leaf. If your leaf works with NissanConnectEV then you can use this app. Right now it's North America only, but I can update that if there's demand.
Here are some screenshots:
If you're interested, send me a direct message and I'll send you instructions on how to try it out. Once I get enough feedback I'll submit the app to FitBit for full publication in their App Store.