It'll be tough to avoid supporting the hardware. If it's provided by you and used to run your application, then you're going to get the support calls.

You can push the client to call the hardware vendor ("we don't support hardware, read your contract, here's the number for Dell"), but that's going to frustrate the client and reflect poorly on your business.

It sounds like a losing proposition unless you price the hardware and hardware support into the cost of your system.