You need to know the FACILITY and PRIORITY of the messages. Syslog allows selection of output device based on the facility and priority of the syslog message. This is often configurable by application. And applications often use one of the LOCAL0-LOCAL7 facilities, so it might be an easy configuration. Can you determine which facilty/priority ?
If the facility and priority are also in use by other linux programs, you wont' be able to for your apps messages into one location, while leaving the others alone. This is a limitation in syslog.
You can use syslog-ng (or other alternatives), or trivial log processing.