I would love nothing more than to be able to enable on-demand GPUs, but unfortunately this is a limitation from AMD right now. We can't do PCIe pass through to a virtual machine, it just doesn't work. This is why our minimum is 8 right now. If you look at all of our competitors, they have the same issue. Even Azure "VM", is 8 at a time, but they are all sold out due to high demand.
It kind of makes sense since their history is only supporting the high end GPUs in their HPC solutions, where they don't use VM's. They've committed to us directly that they will fix this issue.
I updated our pricing page to note this.