parameterized values passed to a groovy build step

[Maven User]

Hi all - 

I have a job that needs to execute a groovy pre- step that sets a global 
environment variable.

Is there anyway to do this?

I have tried the following:

for (nodeproperty in hudson.model.Hudson.instance.globalNodeProperties)
{ 
   println(nodeproperty.getEnvVars());
   nodeproperty.getEnvVars().put("FOO", nextdevversion);
   hudson.model.Hudson.instance.save();
   println(nodeproperty.getEnvVars());
}

and then set:

nextdevversion=NEXT_DEV_VERSION

In the variable bindings - but that just set the global environment 
variable to "NEXT_DEV_VERSION". 

I've tried:

${NEXT_DEV_VERSION}
$NEXT_DEV_VERSION
${env.NEXT_DEV_VERSION}

None of these are the actual parameter.

Is this just not possible?