Cross-device cookie tracking with Universal Analytics?

Question

Is it possible to set a cookie (for my domain) that is tied to a certain user across devices, somehow using the cross-device capabilities of Universal Analytics?

I don't need to know who that user is, just that it's the same person on a different device.

I know I can use Custom Dimensions (formerly Custom Variables) to assign an arbitrary value to a user/session but I need to be able to read it's value. It's a boolean value I need to store so even the fact it exists would be enough.

I hope I've explained clearly but if not let me know!