Hey James, I just happened to be browsing and saw this.
One slave at a time.
If I remember correctly, you can download a new configuration set up to the PXI card to change the parameters of the slave it's emulating, but this takes a few seconds (~10).
This was from an old issue I worked on. After some digging I found the code - it's not the prettiest - but it shows the basics. Essentially you're just modifying the address field of the slave blob.
In the project I used a cRIO PB as the master, so you might see some broken items if you don't have that driver installed. You can ignore that (as it was just the master I used) and focus on the PXI-PCI Slave Main.vi. If I remember correctly, the code was last saved in LabVIEW 2013 SP1.