  We explain how the strategy of solving renormalization problems in HQET
non-perturbatively by a matching to QCD in finite volume can be implemented to
include dynamical fermions. As a primary application, some elements of an HQET
computation of the mass of the b-quark beyond the leading order with N_f=2 are
outlined. In particular, the matching of HQET and QCD requires relativistic QCD
simulations in a volume with L ~ 0.5 fm, which will serve to quantitatively
determine the heavy quark mass dependence of heavy-light meson observables in
the continuum limit of finite-volume two-flavour lattice QCD. As a preparation
for the latter, we report on our determination of the renormalization constants
and improvement coefficients relating the renormalized current and subtracted
bare quark mass in the relevant weak coupling region. The calculation of these
coefficients employs a constant physics condition in the Schroedinger
functional scheme, where the box size L is fixed by working at a prescribed
value of the renormalized coupling.
