I could not find this in the documentation which appears to be lacking...
In any case, port-level shaping is supported on the 3200 and 4200 EX-series as of JUNOS 9.3:
[edit class-of-service] root# set interfaces ge-0/0/40 ? Possible completions: + apply-groups Groups from which to inherit configuration data + apply-groups-except Don't inherit configuration data from these groups
scheduler-map Output scheduler map > shaping-rate Output shaping rate > unit Logical interface unit (or wildcard)