[boost] Crosscompiling context and fiber without multithreading

Dear all, I am developing for a PowerPC target under real-time os und studying a possibility to employ fibers. They seem to be a good fit, since we have a single thread but several entities, which could in fact be considered parallel. Data exchange through channels also is relevant for the project. The problem is, that though we are provided with a quite recent compiler gcc 4.7.4 with c++11 support, the multithreading part of std is missing, since the OS has its own implementation of multithreading functionality different from pthreads and std::thread. Is there any chance to compile context and fiber without multithreading support? Or it is used under the hood and can not be avoided? Best, Vitaly