  It is argued that the ratio of the yield of pairs of charged and neutral
$B^{(*)}$ mesons in the processes $\Upsilon(5S) \to \pi^0 + (B \bar B^* +
c.c.)$ and $\Upsilon(5S) \to \pi^0 + B^* \bar B^*$ is very sensitive near the
corresponding heavy meson threshold to the strong interaction between the
mesons in the $I^G(J^P)=0^-(1^+)$ channel due to significant isospin breaking
by the Coulomb force. This channel, not readily accessible by other means, may
contain near-threshold molecular meson-antimeson resonances --- isoscalar
analogs of the isovector states $Z_b(10610)$ and $Z_b(10650)$.
