Get a 16 or 24 port managed switch that supports vlans (you need a port for each pump plus your laptop)
Put each pump in a separate vlan
Use a descent laptop with parallels or VMWare workstation
Run X number of machines to run the upgrade, each connected to a different vlan (trunk the vlans to the VMs through the laptop NIC (maybe use a USB nic)
Get a little fancy and see if you can script the running of the upgrade so when the VM starts it automatically starts the upgrade process.
Another option that could be wireless would be to use a device that supports multiple SSIDs like a Mikrotik router with wireless.
Each SSID would be a separate vlan/separate pump.
On the pump side use a similar mikrotik device to bridge the wireless and ethernet port. (you might be able to use something like a Raspberry Pi as this client device)