[Distutils] Choice of dependencies?

Is it possible for a package to depend on one of several packages, with the user having the option to pick? For example, my package P might depend on package A, plus either package B or package C. I know I could (ab)use extras_require, but in my case this is a real dependency rather than an optional extra. The other option I have is to just pick one of the dependencies (B or C in my example above), and thereby force people to install it even though it's not strictly required. Neither option seems particularly attractive. John