No this is not possible. The relationship between Moodle and Joomla is one to one.
That said, if you could find a way to run two Joomla's at the same time, then logically (not tested) this would work. For example, a frontend that directs visitors to the different Joomla versions (perhaps users synchronized). Each Joomla version having an exclusive relationship with one moodle installation. Note this may need three Joomla installations. The frontend which directs and then two more for the Moodle connections. Again, this is in theory and never tested nor attempted.
