  We give the analytical expressions and numerical values of radiative
corrections to the covariant derivative operator on the static quark line, used
for the lattice calculation of the Isgur-Wise form factors $\tau_{1/2}(1)$ and
$\tau_{3/2}(1)$. Those corrections induce an enhancement of renormalized
quantities if an hypercubic blocking is applied to the Wilson line, whereas
there is a reduction without such a blocking.
