Setting aside all the negativity (most of it relatively justifiable, even if absurd sounding, and most of it also relatively work-around-able):
- Bricking all the pumps at once (I assume this is being done before/after hours, and there IS a recovery procedure)
- Networking creating sparks that blow the place up (How is hooking up 2 cables to 2 pumps different than hooking up 1 cable to 1 pump)
- Interrupting customers (Again, before/after business hours, or during non-peak hours, and only doing a few at a time)
- Simultaneous hacking exposure (Connecting device doesn't have to be internet-connected, and in that case, how is connecting to one a time different than connecting to all of them)
- Automating yourself out of a job/hourly pay (Nothing wrong with working smarter, rather than harder; applies to just about every career, even with an hourly wage) .. I'd look at something like a small form factor PC (yeah, not as convenient as a laptop) with a couple of quad port NICs.
Run your virtualization hypervisor of choice (VMware ESXi or VMware Workstation, VirtualBox, whatever), and install your vendor's preferred OS and software application as a VM. Clone it many, many times (as many times as you have NIC ports). Give each one of them a single dedicated NIC. Run cables to each pump, and start your engines (that's about as close as I can come to making a gas station pun).
It's a fairly simple solution in that it doesn't require any fancy networking knowledge (VLANs, iptables, NATting, etc), and you're using a very straightforward virtualization configuration that most vendors will agree is supportable (their preferred OS, a single network port, etc).
If you can find a way to setup a couple of quad port NICs on your laptop, you could probably use that as well. In fact, many laptops have the option of purchasing a "docking station" that often have PCIe slots. If that's the case, maybe that's all you need to make the above solution work.
I think that being able to do "4 or 8 at a time", using a solution like this one, would be a huge improvement over doing 8 or 16 of them "one at a time".