Just in case:
If I understand your problem, you could mark the packets both in input and forward chain and it would have the same effect as marking in prerouting.
Then you remove the marking in input leaving only the one in forward?
Just in case:
If I understand your problem, you could mark the packets both in input and forward chain and it would have the same effect as marking in prerouting.
Then you remove the marking in input leaving only the one in forward?