I might not understand your question correct. But, if you use 'discard' instead of 'reject' as your firewall rule action, it will prevent the router from sending the ICMP destination unreachable messages, when the packets are dropped by the filter.
http://www.juniper.net/techpubs/en_US/junos10.3/topics/usage-guidelines/policy-configuring-actions-in-firewall-filter-terms.html
Action Description
discard: Discard a packet silently, without sending an Internet Control Message Protocol (ICMP) message. Discarded packets are available for logging and sampling.
reject <message-type>: Discard a packet, sending an ICMPv4 or an ICMPv6 destination unreachable message. Rejected packets can be logged or sampled if you configure either the sample or the syslog action modifier. You can specify one of the following message codes: administratively-prohibited (default), bad-host-tos, bad-network-tos, host-prohibited, host-unknown, host-unreachable, network-prohibited, network-unknown, network-unreachable, port-unreachable, precedence-cutoff, precedence-violation, protocol-unreachable, source-host-isolated, source-route-failed, or tcp-reset. If you specify tcp-reset, a Transmission Control Protocol (TCP) reset is returned if the packet is a TCP packet. Otherwise, the default code of administratively-prohibited, which has a value of 13, is returned. Supported for family inet and inet6 only.