It is stated in this poster from a 2007 Sciam article (link below) that an observation is not required in a quantum eraser experiment:
"The fringes do not appear if the particles interact with something that could thereby be used to ascertain each particle's location at the slits. For example, a photon might scatter from the particle, and reveal that it went through the right-hand slit. The photon need not be detected - all that matters is that the 'which slit?' information in principle could be determined if it were to be detected."
So it seems that only the existence of the routing information makes a difference. Is this true, and if so, could the experiment be automated entirely?