I was aware of this use case when I wrote the guide and made a patch that solves this case.Basically I modified the poller-wrapper.py to accept group-ids and poll a specific group only.
You can then create a host-group in observium for the remote poller to poll and create another group with "all other hosts" and have poller 1 and poller 2 poll that group instead. Just make sure that all your hosts are in some of these two groups to have them all polled.
The patch was not accepted however as the main plan is to register pollers in the database and be able to control this via Observium in a more controlled manner.
/Markus