[Click] User defined deterministic NAT Table

[Latency Buster]

I am trying to do some pretty basic NATing but with the only
requirement that the NAT mapping table should be user driven. For NAT
I would like to change the tuple (SA,DA) pair to (SA`, DA`) but the
user should be able to drive the mapping from SA->SA` and DA->DA`.
Ideally, this should look something like,  IPAddrMapper (SA - SA` DA -
DA`, ..., ..,).

Is there any existing elements that would allow me to achieve such a
functionality? I looked around IPAddrRewriter() and IPRwriter but they
do not allow the fine control of the address mapping (as I
understand). Else, I am planning to write one.

Thanks,