  The prediction of differential cross-sections in hadron-hadron scattering
processes is typically performed in a scheme where the heavy-flavour quarks
($c, b, t$) are treated either as massless or massive partons. In this work, a
method to describe the production of colour-singlet processes which combines
these two approaches is presented. The core idea is that the contribution from
power corrections involving the heavy-quark mass can be numerically isolated
from the rest of the massive computation. These power corrections can then be
combined with a massless computation (where they are absent), enabling the
construction of differential cross-section predictions in a massive variable
flavour number scheme. As an example, the procedure is applied to the low-mass
Drell-Yan process within the LHCb fiducial region, where predictions for the
rapidity and transverse-momentum distributions of the lepton pair are provided.
To validate the procedure, it is shown how the $n_f$-dependent coefficient of a
massless computation can be recovered from the massless limit of the massive
one. This feature is also used to differentially extract the massless
$\text{N}^3\text{LO}$ coefficient of the Drell-Yan process in the gluon-fusion
channel.
