Some people live on their company's computer and when they leave they do not have one.

Yes, I always add "there is a machine set up for you if you do not have one". That said the machine has a generic setup with most common editors but no plugins. But good engineers will probably have a script on a Github Gist or something like that will setup the machine as they want it.

In general, a candidate with their own setup will do better. I think this is one of the reason that big companies do not let people use their computer.

That's exactly how I do it. My goal is to assess the candidate's skills with realistic expectations, a whiteboard is a tool he or she can use, not the goal of my interview. If he can write code on a whiteboard and he doesn't know how to compile a program, it rings a bell.

So get one. You can get a good one from the pawn shop for $200. You can afford that if you're interviewing for a 6 figure job.

Edit: I'm not kidding. I've bought $200 laptops from the thrift store, usually for travel purposes so I don't worry about losing/breaking it.