Adding Flights to PNR

So here is the situation. I have a large PNR with multiple tickets and need add a few segments in the middle

Ticket n:
SFO-SEA 7pm 8-AUG

I now also need to fly:
SFO-AUS-SFO ... connecting to my current SFO-SEA flight

Is there a way to link them together so that if there is IRROPs on the AUS-SFO leg I have a good way out