  A new route to $d^0$ magnetism is established with help of the first
principles methods. Non-magnetic interstitial impurities from group 14 in the
periodic table are found to induce $p$-orbital magnetism in polycrystalline
PbO-type structures. The half-filled $p$-orbitals occupied by two electrons is
generated on the impurity site for which the ferromagnetic state of high
stability is guaranteed by the first Hund's rule. Since the impurity is
embedded between layers of the host, its atomic radius is a key to tune not
only its solubility but also the magnetic behavior: the on-site stability of
the spin polarized state grows with reduction of the atomic radius while losing
in the long-rang order interactions. However, for impurities of smaller radius
the weaker inter-site magnetic coupling can be compensated by their
concentration as the impurity solubility limit is shifted to higher magnitudes.
