Hi,
I've just submitted a pull request in the hope that you will consider a patch to add a Super Simple Gimbal drive mode into the APM code. Pull request is here:
There are details of what the patch is and does and some testing videos that myself and a friend who designed a 3d printable super simple gimbal have done.
If there is a nicer / better way to do it, or any adjustments / improvements you would like to see, let me know and I'll do my best to implement them. Either here, or in the github issue.
This is my first attempt to create a patch for Arudcopter so be kind :-)
Thanks,
Rob.