How to use substr in a choose statement for BI Desktop

This is for BI Desktop RTF for JDE 11.1.1.7

I am trying to use the substring function inside a choose statement.

Another developer did this in a form field:

<?choose:?><?When:$ENV = 'JPD910'?>
Which of course fails every time they upgrade until it is changed.

I am trying to do something like:

<?choose:?><?When:xdofx:substr($ENV,1,3) = 'JPD'?>
This is to prevent release specific check. If it is not production then it prints Void and test on the check.

Any ideas?

Thanks,

Dan