Ten atom clusters of X = Si, Ge, Sn and Pb are known to be magic, suggesting that addition of an atom to such clusters is generally unfavorable. However, here we report using an ab initio ultrasoft pseudopotential method that these clusters can be further stabilized by doping of a Ni or Pt atom, leading to some of the smallest metal encapsulated clusters of these elements. For Si and Ge, doping of Ni is optimal while for Sn and Pb, Pt is the best. Our results agree with the recent observations of strong abundances and magic nature of X10Co- clusters of these elements. These findings could lead to the development of novel cluster-based nanomaterials for optoelectronic and other nanoscale applications.