Perhaps you can use the OnObjectExit or OnObjectModify script triggers along with a script that uses Refresh Portal
I have two portals showing information from the same table. When entering a new record in one portal, associated information showing in the other table does not appear.
It won't until you commit the parent record. Ron's suggestion of a Script Trigger is workable; you will need to use Commit Record / Request and then return the user back to the record he was editing before the commit (because committing causes the portal to lose the row focus).