How can one get multiple GPUs to be assigned to the same Vulkan physical device group?

We have a setup with 4 Tesla GPUs, but when vkEnumeratePhysicalDeviceGroups gets called, the Vulkan API returns 4 device groups, each with one Telsa GPU.

How can one build a system with multiple GPUs, such that 2 or more GPUs will be assigned to the same device group? Does Nvidia have a suitable board with 2 or more GPUs? Is an SLI-capable motherboard required?

Any suggestions would be most appreciated.

Robert Lasater