Doing a printed version of http://www.thingiverse.com/thing:248009/ i realized the servoarms are harder to mount than i thought.
Therefore, using the arms from http://www.thingiverse.com/thing:250204 and the servohorn http://www.thingiverse.com/thing:42796 added a servohornsized cutout.
A 9g servohorn fits into the hole and can be mounted using two screws.

I print 2 arms and mount them using 2 scews leaving the screwhole in the middle unused.