If you could send the air down in rigid containers - like ping pong balls - that could themselves withstand the outside pressure, the air inside would retain its negative buoyancy at the required depth. The problem would be getting a container that did not weigh so much itself that the air's buoyancy raised only the container.

Of course, if you could find containers that strong, you could evacuate the air inside them and give them even more buoyancy.

Easier to leave the ship there, chaps.

p.s. Sir Lew Grade, whose company lost a motza on the "Raise the Titanic" movie, is reported to have said, "It would have been cheaper to lower the Atlantic!"