From the proposals and implementations, I will try to learn any simple way to add a pass that  will target any layer and create a sub-graph (At graph layer) before gradient computation.
Such an addition, will help third parties to describe the computation differently and closer to a dedicated engine (we are interested in FPGA kernels): the computation is similar to to CPU, possibly using the same basic operation and changing  the order.
The introduction of fake quantization nodes is  one way we pursue to modify the subgraph. But our fake nodes will affect the forward and the backward.