This contribution is addressed to the dynamics of heterogeneous interacting agents evolving on the plane. Heterogeneity is due to the presence of an unfiltered externally controllable fellow, a shill, which via mutual interactions ultimately drives (i.e. soft controls) the whole society towards a given goal. We are able to calculate relevant dynamic characteristics of this controllable agent. This opens the possibility to optimize the soft controlling of a whole society by infiltrating it with a properly designed shill. Numerical results fully corroborate our theoretical findings.