calculating an aspect of shared buffer state from a background worker

I'm looking at doing a calculation to determine the number of free buffers available.  A n example ratio that is based on some data structures in freelist.c as follows:

(StrategyControl->lastFreeBuffer - StrategyControl->firstFreeBuffer) / (double) NBuffers

Is there a way to get access to the StrategyControl pointer in the context of a background worker?  

Thanks,

Robert