  Fragmentation of an interacting Bose gas refers to the macroscopic occupation
of a finite set of single-particle eigenstates. This phenomenon is related to
the notion of particle-number squeezing in quantum optics, an exquisite
property of quantum states that can offer metrological gain. So far,
fragmentation has only been partially achieved in experiments involving a large
number $N$ of bosons in few modes. Here, we introduce a practical and efficient
scheme to prepare fragmented states in systems realizing the $L$-mode
Bose-Hubbard model. We demonstrate how a large energy detuning between the
modes can be used as a practical control parameter to successfully fragment a
Bose gas over an extremely short preparation time. Applying an optimal-control
approach within realistic experimental constraints, we obtain total
fragmentation at a high filling factor, realizing $\ket{N/L,...,N/L}$ Fock
states with hundreds of bosons in very few modes over a few tunneling times.
