I've never solved a ghost cube, so you're ahead of me, but if you found a picture would you be able to look at the shape of the corners that you have and the shape of the corners in the picture to figure out relative position?
If you can find a picture of the solved cube and place 2 or 3 corners you might be able to place the rest on the basis that the other corners have facets that are on other faces of a cube (parallel or perpendicular to faces of the centers already placed).
That's so-called 'void cube parity'. Easiest way to solve it is just to swap the unsolved pieces, but you can also rotate the centers in any middle layer ('rotate' meaning to take the centers off and put them on the adjacent side, like you're turning the slice without moving the edges).
It happens because rotating the centers in a layer one turn is the same as rotating the edges, which means it's a direct cycle of an even number of edges, which you can't do. That gives you PLL parity.