Hi Ross,
I think that Andrew’s last comment on DJI M210/M210(RTK) Dual Gimbal Support is answering your questions above:
https://community.pix4d.com/t/5886/comments/360000562423
To sum up there is no easy workaround that can be done for the moment and it is not guaranteed that it will work. Don’t hesitate to feedback us if you take the opportunity to test the dual downward-facing gimbal anyway.