Could a local group X-ray halo affect the X-ray and microwave backgrounds?

Suto et al. have suggested that an X-ray halo in the Local Group might explain both the observed low-energy excess in the X-ray background and the quadrupole anisotropy in the cosmic microwave background. Recent observations of poor groups of galaxies by the ROSAT PSPC set reasonable limits on how extensive and dense such a halo could be. The poor groups most similar to the Local Group do not have a detectable halo, and the upper limits of these observations suggest that any Local Group halo would be nearly 2 orders of magnitude too tenuous to produce the effects that Suto et al. discuss. In particular, the Sunyaev-Zeldovich effect cannot contribute significantly to the quadrupole anisotropy measured by COBE.