  We utilize a glass-like structural transition in order to induce a Mott
metal-insulator transition in the quasi-two-dimensional organic charge-transfer
salt $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br. In this material, the terminal
ethylene groups of the BEDT-TTF molecules can adopt two different structural
orientations within the crystal structure, namely eclipsed (E) and staggered
(S) with the relative orientation of the outer C$-$C bonds being parallel and
canted, respectively. These two conformations are thermally disordered at room
temperature and undergo a glass-like ordering transition at $T_g \sim 75\,$K.
When cooling through $T_g$, a small fraction that depends on the cooling rate
remains frozen in the S configuration, which is of slightly higher energy,
corresponding to a controllable degree of structural disorder. We demonstrate
that, when thermally coupled to a low-temperature heat bath, a pulsed heating
current through the sample causes a very fast relaxation with cooling rates at
$T_g$ of the order of several 1000$\,$K/min. The freezing of the structural
degrees of freedom causes a decrease of the electronic bandwidth $W$ with
increasing cooling rate, and hence a Mott metal-insulator transition as the
system crosses the critical ratio $(W/U)_{c}$ of bandwidth to on-site Coulomb
repulsion $U$. Due to the glassy character of the transition, the effect is
persistent below $T_g$ and can be reversibly repeated by melting the frozen
configuration upon warming above $T_g$. Both by exploiting the characteristics
of slowly-changing relaxation times close to this temperature and by
controlling the heating power, the materials can be fine-tuned across the Mott
transition. A simple model allows for an estimate of the energy difference
between the E and S state as well as the accompanying degree of frozen disorder
in the population of the two orientations.
