Set PersonWantsOrg properties to mandatory for specific products

This seems like it should be straight forward, however I haven't been able to find a simple solution to the following:

There are a number of ootb fields on the PWO records which are used to capture details during the request - Reason, Valid From and Valid Util.

Is there a way of setting these fields to be mandatory for specific AccProducts?

IE product A requires Valid To field to be populated, product B this can remain optional.

We are able to create a request property which maps to the Valid Until field with the mandatory flag enabled.  This works for the end user, as they are prompted to complete the field on raising the request - however the approver then sees 2 Valid Until fields both containing the same information.

Any ideas?