I've added an option for using PPE threads in addition to the SPEs, however the results are somewhat underwhelming. The Cell PPE is effectively a dual-core processor, but even with two PPE threads I only see about an extra 500 Khash/s.
There may be some PPE optimizations I'm missing, but otherwise I'm currently maxed at about 21.983 Mhash/s using all six SPEs and two PPE threads.
For those interested, I've put the source code online:
https://github.com/verement/cellminerFeedback and donations welcome. (Donations to: 18xDLQsJ94ihhx5YovqAhVY2b9SC5b81h)
Cheers.