In a conventional war? There is not much Pakistan can do except diplomatic support.
The real question is, what if some nutjobs in Israeli establishment (believe me, there is no shortage of them, secretly or not) decide to use a nuclear weapon against Iran? What will Pakistan do after that? Is it ready to nuke Israel in return? Or at least lend some weapons to Iran to use them on Israel? That would be the best help and I think we can count on Pakistan in that scenario, because the situation would be too much 'out of control' and all the rules of warfare will change after such scenario.
But nonetheless, Israel can't and won't do $hit on its own and without U.S help.