Possibly more relevant:
http://blogs.sun.com/foo/entry/i_want_to_see_my
Apparently the JSP-processing
servlet defined in the Glassfish domain's
config/default-web.xml supports an optional <init-param> named
keep-generated that you need to set to "true". The source code should then get written into the domain's
/generated/jsp directory structure (under the relevant app's subdirectory).
The default-web.xml has comments explaining all the JSP-processing servlet's init-param options, including a saveBytecode option for keeping the resulting class files as well (though it says that depends on JDK 6).
The blog article referenced above says that you also need to specify precompilation of the JSPs when deploying the app, but I'd be tempted to try it "normally" first (might be something the author needed but doesn't apply to your situation; or might depend on which version of Glassfish; or which of the various deployment mechanisms you use etc).