I haven't been paying attention so perhaps this has been mentioned before,
but why don't you send a "packet" from your "=" block, and have each block
it passes through on the "ring" add the TEXT of the block value to the
packet, a sort of "record route" function.  When the packet gets back to
the "=" block, You'll have a text expression that can be computed using
standard math parsing routines.

BillW