Let's say you happen to be a mathematician, and your spouse is also an academic and in a humanities field in which there are very few jobs advertised. Assuming that you can convince universities to hire you on a tenure-track level, what are the chances that they will be able (or willing) to create a position for your spouse? If you already have a job that you are reasonably happy with, is it at all reasonable to apply to positions where there is nothing advertised for your spouse in the area in hopes that you can arrange something for them if you get a job offer?

I'm mostly interested in the US and research I-esque jobs, though I would be happy to hear about the situation in other countries.