A local jeweller has a Canon EOS 550D with a telephoto lens model 'Canon EF 75-300mm (f/4-56 III USM)' which she's using to photograph her work for sale.

The lens will zoom enough to get large enough images for her purpose, however, the minimum focal distance of this lens is 4.9 feet so she has to take the pictures from across the room.

Is it possible to use this lens for closeup work with an extension tube or add-on diopter lens, or is it a dead loss for this purpose?

The objects she photographs are typically 2 inches in radius, and she needs a DOF of 1 to 2 inches depending on the piece.