Having been in a similar situation, I feel qualified to add in my $0.02. My BS and MA degrees are in Math, but my PhD is in Industrial Engineering. The easiest thing you can do is simply write the search committee and ask if a PhD in a related field is acceptable.

There are multiple advantages to this approach. The most obvious is that they will save you time putting together a packet if the answer is no. Additionally, you get a chance to put a bug in their ear, so that your application will not be coming out of the blue. Finally, you will be able to trump up the advantages of having a degree in a closely related field. In my case, many of the schools I applied to had large teacher ed programs, and I was able to tout my rather large stockpile of practical applications of just about any mathematical topic.

That said, it still can be a tough sell. Over the course of two years, I had four on-campus interviews (one was a visiting position) without an offer. And I was coming in having successfully written a large NSF grant, a pair of journal articles in review, and glowing teaching evaluations.