Partner's hand was: AQJ10975 1095 5 K8
Best contract is 7S making on 3-2 clubs or on 4-1 clubs if the lead is the (conventional wisdom) trump.
So a 4S bid won't do the job.
Can one get to the grand after 4D?
Well there is a cue bid available, that being 2NT. Granted that would only be reasonable with 4 card support. With only 3 card support one might chose to defend or perhaps even double with sufficient values. That is why I think a natural interpretation is more useful.
Some thoughts:
Patrick: the hand you ask about (4-4 in the majors) would have made a negative double over 1 Diamond.
Aviv: Your game try hand is very reasonable. So what is North to do with a minimum hand with 4 spades. There could still be a 4-4 Spade fit ...
Rick: If I were cheating I certainly would change the meanings of the various signals from one event to another (maybe within the same event). I might even use a whole different set of signals. Extrapolations from one event to another may prove to be difficult.