I believe this would be the RP conf file stanza you would need to use to accomplish this...It could also likely be done with the WAF rules as well, but this is likely a lighter weight option...
[validate-headers]
# This stanza is used to list those headers which should be validated
# on each request. The format of each configuration entry is:
#
# <hdr> = <value>
#
# For example to ensure all requests are from www.ibm.com set:
#
# host = www.ibm.com
#
# If multiple headers of the same name are configured, the corresponding
# header in the request must match one of the configured values