If you calculate the signed difference of the angle of the objects every tick and add that to a variable you can get the total degrees moved around the center object.
signed angle difference of b to a = angle(0,0,cos(b-a),sin(b-a))
Example showing the total degrees moved around the center object.
https://dl.dropboxusercontent.com/u/5426011/examples21/signed_anglediff_sum.capx