My working solution (for iOS or Android):
+ Set Orientations in Properties to Any
+ Add Browser-Plugin
+ Add Action on game start: Browser -> Lock Orientation to ... (what you need)
You can change the orientations at runtime.
EDIT: You don't need this Plugin:
.. but you can use it instead of the browser plugin.
The plugin worked great! Is there a C2-compatible version, please?
The browser method is what I have been doing from the start. I tried it again and it didn't work on Android.