Flying the straight C with the 1S1's it was company procedure to match N1's, which 95% of the time was the primary limiting factor, and simply accept the slight indifferance in fuel flow readings. The difference as A Charlie stated is really not likely to be significant...
Don't know how your regs differ over there Clearance but here in the UK we were prohibited from X-feeding during Public Transport ops except in the case of an emergency...