If I had a known unused one, I would absolutely not use it until Intel finishes putting out their patch to motherboards to address this. You have no idea whether you could cause damage that won't be detected, leaving you with a slightly damaged processor that malfunctions occasionally.

Intel may publish guidance on how to use unpatched processors. If they don't -- they sure have not been forthcoming with information thus far -- here's my own suggestion.

When I do use it, I would, prior to booting any OS on the CPU, go into the BIOS and turn everything related to the CPU to minimal performance. Memory speed down, disable Intel turbo boost, everything. If you can disable cores there, disable all but one -- even my severely-damaged pair of CPUs could still boot without corrupting my root filesystem as long as I ran using only a single core (though two cores induced problems), and I'd take that as an argument in favor of one core being preferable, though I cannot say for sure that doing so helps avoid damaging the chip rather then just avoiding being affected by the damage once incurred.

And the first thing I'd do, booted into that minimal-performance-CPU-environment, would be to do that motherboard BIOS update. Then go back and reset the motherboard to defaults and use the thing normally.

Maybe that's over-cautious, but we know that the processors destroy themselves with use, and we have no idea what the minimum amount of time -- if any -- to incur damage is. Unless Intel can come out with some kind of diagnostic to reliably detect damaged CPUs, you won't know if you damaged your CPU in that window before the BIOS update, and it is maybe occasionally corrupting data, which I'd guess is a situation that you probably don't want to be in during the lifetime of the CPU.