I would suspect the capability is nearly there. On the P-6' cousin, the OB-6, it is possible to enable an Arpeggio over a Sequence. This is capable, if you have the desktop module. If you have the OB-6 module, mapped to a keyboard… have at it. You can map the Sequencer Start/Stop via the NRPNs in the Manual. Do the same with the Arp Stop / Start NRPNs. With these mapped to your controller – you can start a Sequence, then enable the Arpeggio for your patch. Holding keys will fire off your arpeggio, during a sequence..
Order matters. You need to fire up the Sequencer first, then the arpeggiator. Like I said, this is on the OB-6 desktop module. I have things mapped to my Axiom Pro 61.
Since the P6 shares these internal bits with the OB-6, I wouldn't be surprised if the capability isn't hidden inside the P6 too. In any case -- it seems the art of the possible, is nearly there, with both these instruments.