  In the subclass of high-mass X-ray binaries known as "microquasars",
relativistic hadrons in the jets launched by the compact object can interact
with cold protons from the star's radiatively driven wind, producing pions that
then quickly decay into gamma rays. Since the resulting gamma-ray emissivity
depends on the target density, the detection of rapid variability in
microquasars with GLAST and the new generation of Cherenkov imaging arrays
could be used to probe the clumped structure of the stellar wind. We show here
that the fluctuation in gamma rays can be modeled using a "porosity length"
formalism, usually applied to characterize clumping effects. In particular, for
a porosity length defined by h=l/f, i.e. as the ratio of the characteristic
size l of clumps to their volume filling factor f, we find that the relative
fluctuation in gamma-ray emission in a binary with orbital separation a scales
as sqrt(h/pi a) in the "thin-jet" limit, and is reduced by a factor 1/sqrt(1 +
phi a/(2 l)) for a jet with a finite opening angle phi. For a thin jet and
quite moderate porosity length h ~ 0.03 a, this implies a ca. 10 % variation in
the gamma-ray emission. Moreover, the illumination of individual large clumps
might result in isolated flares, as has been recently observed in some massive
gamma-ray binaries.
