How could Jellicoe keep the plan secret from Russia?

How could Jellicoe coordinate with Russia without letting the secret operation leak?

He would withhold the plan until the Grand Fleet was entering the Danish Straits, then notify Russia in time for its Baltic Fleet to sortie later that day.

Russia, France, and other allies would learn about the operation only after it had begun. A message sent around midnight as the Grand Fleet passed Copenhagen could announce that the Royal Navy had entered the Baltic. The Russian admiral would then mobilize quickly, attracted by the prospect of a decisive joint battle. The fleets would lose some early coordination, but Russian arrival during or after the main action could still transform the outcome. Using troops already outside the Western Front would reduce the number of allied governments that needed advance warning. Operational control and secrecy are gained at the price of coalition trust and carefully synchronized opening moves.