The Soviets tested this for very outsize cargo - spacecraft components.
The developers considered using a couple of Mil Mi-26 helicopters to "bundle" lift the Buran, but test flights with a mock-up showed how risky and impractical that was.
This site (cited in the quote above) goes into a little more detail:
The newly developed MI-26 helicopter of the weight-lifting capacity of 26 tons was offered for delivery by helicopter. According to this project, bulky cargoes of high mass (airframe and rocket bays) tied with cables had to be carried by 2 or 3 helicopters, and such ‘bundle’ had to move along the route, at the best fit height and flying speed. As the basis for such version the example of helicopters application for ‘crane’ operations was brought, but there was still no experience of flights ‘in bundles’.
Test flights with mock-up cargo having the configuration of a tank section of the rocket were carried out at LII. The tests revealed a complexity and risk of such kind of delivery. During one of the flights at a suddenly arisen weak turbulence of atmosphere, a ‘pendulous’ swing of cargo on the cables started which caused a disturbance of the helicopters flight stability, owing to what the crews were compelled to dump the cargo.
The natural way to lift something like this would seem to be seperate slings at the two ends, which would counteract the side force problem but at the cost of having the two helicopters very close. Three would complicate it even more!