filtering ICMP *codes* with PIX?

["Razvan Peteanu" <rpeteanu () sympatico ca>]

First, thanks for the useful thread on ICMP tunneling. Now, related to this, a client has a PIX 4.2.2 and I was  
wondering how to
filter different ICMP *codes* (in order to allow path MTU discovery (Type 3, code 4) but deny traceroutes (again type 3 
but code 3).
The official doc doesn't even mention conduit  syntax for ICMP and the online help as well as the recently published 
book "Cisco
Security Architectures" describe the syntax as:

    conduit deny|permit icmp <g_ip> <g_mask> <f_ip> <f_mask> [<icmp_type>]

which suggest a filtering on the type field only. Any feedback is appreciated.

Thanks,
Razvan