It depends on how the JSP pre-compilation process works for appserver you are pre-compiling for.
I would imagine the WAR needs exploding first, if this is the case then you could add another dependency on the "incremental-tomcat" target in build.xml. This target could then run the process after the WAR has been deployed.
This is something we are considering adding to the build scripts in the future, but if you get something working, let us know, we could add it sooner