  As shown in Ref.\cite{Rod09}, the Fermi nuclear matrix element $M^{0\nu}_F$
of neutrinoless double beta ($0\nu\beta\beta$) decay can be reconstructed if
one is able to measure the isospin-forbidden single Fermi transition matrix
element from the ground state of the final nucleus to the isobaric analog state
(IAS) of the initial nucleus, for instance by means of charge-exchange
reactions of the $(n,p)$-type. Here, simple estimates for $^{82}$Se are made
which show that indeed the tiny cross section $\sigma_{np}(0_f^+\to IAS)$ is
dominated by the admixture of the double IAS in the ground state of the final
nucleus provided that the isospin mixing is weak and can be treated
perturbatively. A measurement of such a cross section would definitely be a
very difficult task, but it can advance a lot our knowledge of the
$0\nu\beta\beta$ nuclear matrix element.
