You should configure the slave listeners for different ports.
Master should listen on port 80, as you have done.
The slave for www.thisplace.com should listen on one port, say 8080.
and the slave for www.thatplace.com should listen on a different port, say
8081.
http://www.thisplace.com:8080 and
http://www.thatplace.com:8080 should both display content for
http://www.thisplace.com
http://www.thisplace.com:8081 and
http://www.thatplace.com:8081 should both display content for
http://www.thatplace.com
and http://www.thisplace.com and http://www.thatplace.com should each
display the correct content.
