  We consider a model in which massive stars form in a self-gravitating
accretion disk around an active galactic nucleus. These stars may evolve and
collapse to form compact objects on a time scale shorter than the accretion
time, thus producing an important family of sources for LISA. Assuming the
compact object formation/inspiral rate is proportional to the steady-state gas
accretion rate, we use the observed extra-galactic X-ray luminosity function to
estimate expected event rates and signal strengths. We find that these sources
will produce a continuous low-frequency background detectable by LISA if more
than >~ 1% of the accreted matter is in the form of compact objects. For
compact objects with m >~ 10 Msun, the last stages of the inspiral events
should be resolvable above a few mHz, at a rate of ~10-100 per year.
