Out of the box, nothing available that I’m aware of.
Expect this could be done, following the maintenance agreement, with a custom portlet that lets you pick the user and their proxy. Upon saving change, a GEL scrip based process would update the necessary.
I don’t know the table/fields involved, but we did something similar for updating usernames. Previous versions of CA PPM didn’t allow one to change usernames after connecting to LDAP. So, we created a custom portlet with an attribute/lookup to pick existing users, and a text attribute to type in their corrected username. On save, a workflow process with GEL script writes the updated username from our custom text field into cmn_sec_users.user_name.
Then just limit access rights to the new portlet to those that should see it.
Dale