  As the Advanced LIGO and Advanced Virgo interferometers, soon to be joined by
the KAGRA interferometer, increase their sensitivity, they detect an
ever-larger number of gravitational waves with a significant presence of higher
multipoles in addition to the dominant $(2, 2)$ multipole. These higher
multipoles can be detected with different approaches, such as the
minimally-modeled burst search methods, and here we discuss one such approach
based on the coherent WaveBurst pipeline (cWB). During the inspiral phase the
higher multipoles produce chirps whose instantaneous frequency is a multiple of
the dominant (2, 2) multipole, and here we describe how cWB can be used to
detect these spectral features. The search is performed within suitable regions
of the time-frequency representation; their shape is determined by optimizing
the Receiver Operating Characteristics. This novel method has already been used
in the GW190814 discovery paper (Astrophys. J. Lett. 896 L44) and is very fast
and flexible. Here we describe in full detail the procedure used to detect the
(3,3) multipole in GW190814 as well as searches for other higher multipoles
during the inspiral phase, and apply it to another event that displays higher
multipoles, GW190412, replicating the results obtained with different methods.
The procedure described here can be used for the fast analysis of higher
multipoles and to support the findings obtained with the model-based Bayesian
parameter estimates
