You can bond -V to GND, if it's okay with your circuit and testing.
You really shouldn't be using BNCs there anyway, the current handling is awful. Who supplies DC over coax, anyway?
I don't know what all things have 1.5" centers (or three in a row, where you need to use the outer pair, as in this case), so I don't know how appropriate (or not) that actually is.
If you're dead set on it, then yeah, might as well make one. Or at least use extension jumpers of some sort (I don't suppose there's such a thing as a 0.75" offset 'S' bend shape?).
Tim