  We calculate the cross section for q(\bar q)g-production in diffractive DIS
with finite fermion masses and zero momentum transfer. The calculation is done
in the leading log(1/x_p) approximation and is valid for the region of high
diffractive masses (small beta). We apply our cross section formula to
diffractive charm production at HERA: in a Monte-Carlo-Simulation of
diffractive D*+- meson production we include both massive q(\bar q)- and
massive q(\bar q)g-production, and we compare with preliminary H1 results.
After adjusting an infrared cutoff parameter of our model which affects the
overall normalization of the cross section we find reasonable agreement with
the data. In particular, the slope of the beta-distribution can be reproduced.
