A particular OEMed component in my Java application is licensed for a
single CPU. It runs in its own JVM (as a standalone program  - not in
a app server or servlet runner etc). Java 1.4.X. Solaris 5.8

I need the flags to pass to the JVM or other techniques to set the
affinity of this JVM to a single CPU - before the JVM is launched. (
i.e techniques that detect the PID of the already launched JVM and
then set CPU affinity wont work for us but perhaps a small wrapper
java program that makes a system call and then launches this component
etc)
Looking for some pointers where people have done this reliably.

Just affine the shell you launch it from by doing psrset -b $$. 
affinity is inherited.