Caller <--> (internal_IP) Kamailio (external_IP) <---> Callee


I have this set up of kamailio with 2 interfaces.

i use topos module for topology hiding and what i want to do is to
send  external_IP in Contact Header of request relayed to Callee and internal_IP
in Contact Header of response relayed to Caller.

i noticed that :
when i use topos module with contact_mode to 0
all Record-Route and Caller Via Header are removed and thats great.
but i dont find way to put 2 different  ip addresses in Request and Response Contact Header?

when i use contact_mode to 2 Record-Route and Caller Via Header are not anymore removed thats bad for
topology hiding. And its seems we can not use $xavu(_tps_=>contact_host)  parameter of module
to put 2 different  ip addresses in Request and Response Contact Header.


What i want is :

- remove all Record-Route and Caller Via Header for request like when contact_mode to 0

- and put 2 different  ip addresses in Request and Response Contact Header

is it possible to achieve it ?

Thanks.