Those Furutech plugs with a hexagonal cross-section could be tightened and loosened with a spanner placed across the flats, but if the sockets are too close together that won't be possible. Nor will it be possible just by using one's fingers.

An alternative might be to use Neutrik plugs, which will grip like there is no tomorrow, but again, these are not really suitable if one has a weak grip.

I think the only real solution is to follow Kevin's suggestion of using soft nose pliers whose jaws have a semi-circular shape of ~8mm in diameter.