As a courtesy, we waive all instructor fees for solo flight while students are awaiting their "bit of paper". So they can go solo, but they can't take a passenger for a few weeks.
Might be worth asking if your school does the same?
I would question the legality of this, especially in view of insurance. We had the following situation: A student has a signed flight authorisation from his instructor to fly to the location where his examiner is waiting for him. He passes his test, is therefore no longer a student. How does he return to base?
What
used to happen is that the instructor would give him a flight authorisation such that he could return to the base - which is in effect what you are doing. However on one instance, the newly fledged PPL made a poor landing on return from his Skills Test, damaged the plane quite severely and the insurance refused to pay because the pilot was not in possession of a licence nor was he a student......