Actually the BBB FAQ is very clear on this...
Q. Can psychic powers (like Fear of the Darkness) or
other special rules (Imperial Guard Officers’ Leadership)
and pieces of wargear (like Psychic Hoods) be used
from within vehicles by models that are being
transported?
A. As transported models are not physically on the table,
they cannot do anything (unless differently specified).
The only exception is firing weapons (and using psychic
powers and abilities that replace firing a weapon) from
one of the vehicle’s Fire Point or from an open-topped
transport. On the positive side, transported troops
cannot be targeted by the enemy (the enemy can of
course target their transport, and the passengers may
suffer consequences as a result).
[emphasis mine]
A transported model is not on the table and, unless explicitly stated otherwise, may not do anything or use any special rules or wargear, but may shoot or use shooting based powers out of fire ports.
So, from my reading, no you may not use Rites of Battle until the model hits the table. Just like how an IG officer can;t use the vox casters to convey his leadership if he's in a transport.
Call it fog of war (they can't see that it;s really him giving orders) or maybe the comms in the rhino are insufficient to channel all the info he needs to give his all as far as command goes and the hull is too thick to recieve through. Whatever fluff you need to justify it, the FAQ seems pretty clear in that unless it explicitly states otherwise, models in transports are in limbo and effectively don;t exist until they hit the turf.
