How about using the jspc utility (jsp compile)?
This is a script provided by Tomcat for precompiling jsps. To execute, supply the name of the JSP you wish to compile, e.g:
# $CATALINA_HOME/bin/jspc.sh $CATALINA_HOME/webapps/myFile.jsp
An equivalent .bat file is provided for Windows users.
Use a script or
Ant to compile all jsps in a directory.
By the way, Tomcat 6 provides the ability to serve up the old version of a jsp until it compiles the new version.
You may want to read this:
Apache Tomcat 6.0 Jasper 2 JSP Engine How To Scroll down to "Web Application Compilation"
Cheers