How to generate uuid for a soap script that is constant

I use soap ui pro, need to generate a uuid for a testrun

I generate uuid by adding properties, store it in a variable 

${=java.util.UUID.randomUUID()

When i use this in the script, it generates the correct value.  I need to use the same id throughout the run. when I use the above command, each step is generating a new uuid.  how do i overcome this issue.