Route internet traffic via proxy

Hi guys,

I am working on a setup in which some VMs have internet connectivity via VRouter but one the requirements is to hide public ip address to those machines.
Therefore I would like to have something like the following:
VM > Virtual Router > … (internet) … > remote proxy > … (internet)

I already have geo-distributed proxies, however I was not be able to properly configure VRouters to redirect non-local packets to the proxy.
There is almost no information about it and some users suggest to use ip tables but did not worked for me.

Anyone with a similar setup who could share ideas?