The Net-ENI supports only point-to-point DF1 in its EtherNet/IP to DF1 translation mode, so the Net-ENI is always Node 0 and the SLC/MicroLogix is always Node 1.
If you were to set up the DH485 so that the SLC-5/03 is Node 2 and the PanelView is Node 1, then enable DF1/DH485 passthrough, then you *might* be able to download to the PanelView. But you wouldn't be able to go online with the SLC.
What might work is if you set up the 1761-NET-ENI as a generic Virtual Serial Port, so that you're using the DF1 Full Duplex driver (set for a KF3/KE Device Type) instead of the Ethernet driver.
That would allow RSLinx to send out packets with destination nodes 0-31 on them, which would browse the DH485 network via the Passthrough function.
Unless this was the only possible way to access the system, I wouldn't do it; carrying memory cards out to the machine is the best workaround (as long as your PV900 Standard has v3 or later firmware.... the PanelView 900 went out of production years before the rest of the terminals).