Relaxed scan of Cp-M torsion angles of piano stool compounds
I would use the dummy, define the 3 X 10 11 (16 and 18 too) dihedrals in the connectivity matrix, run the optimization and later write a shell script for running subsequent calculations in separate files replacing the value of the previously defined dihedrals. So I guess my solution is only slightly above doing it by hand but so far I haven't found any software that does this and G09 has no workaround.

I hope this helps