squid between haproxy and backend server (no replies)

Hi,

I am using haproxy for path based routing and am trying to forward
traffic to another datacenter under certain conditions. However, the
traffic must go via explicit proxy server (squid). The traffic is
getting forwarded to an https endpoint in AWS fronted by ELB.

Is there a way to define "via proxy" in backend configuration? I did
configuration search, mailing list archive search and google search
but couldn't come up with anything.

Or is there any software which can forward traffic via squid to
another endpoint. (I checked stunnel but didn't find such feature)

Thanks for guiding me with ideas or pointers.

Regards,
Vivek