How to tighten a nut on a threaded rod from the side, through a hole in a hollow tube?

Picture a threaded rod, with a hex nut on it. The rod is inside a hollow tube. You move the nut down the rod by inserting an outside hex wrench into the hollow tube from the top. But what if you only have access to the rod from the side, through a hole in the tube (which is fixed and can't rotate around the rod)? Is there a way to tighten a nut down a threaded rod from the side through a hole in a tube?

Context: the application would be a grip for a fencing weapon. The base of the blade of a fencing weapon turns into a threaded rod (the tang). The bell guard (metal disc to protect your hand) has a hole in the middle, and is inserted onto the tang. The standard grip is a straight tube-ish thing (usually solid except for a hole the diameter of the tang). You stick the tang through the central hole in the grip. Then you stick a nut on the end of the tang (which just extends beyond the end of the grip) and tighten the whole assembly down.

Some special grips are curved, which means that you have to bend the tang in a curve to match the grip first in order to fit it onto the tang. Another kind of grip is straight and hollow, with a plate with a central hole over the end butting against the bell guard, to give the nut a surface to press against, and the tang is cut much shorter than the grip, and you tighten the grip with an outside hex wrench from the back end of it, as I described initially. The advantage is that a shorter tang weighs a lot less, and the weight savings can be really good in fencing. I want to combine the advantages of these two types of grips- a curved grip, which is hollow and lightweight, with a tang that is shorter than the grip itself. Obviously, it would be impossible to tighten the hex nut through a curved grip, hence my question. 

Straight no problem, plumbing section in the hardware store has the tools you need.
Curved now to much, especially not with limited space.
If there is enough space left for a tube spanner then you could coul it and weld it to tube bending spring that still fits over the tang.
I might try using some bismuth though....

Yes. You don't use a hex nut, but a threaded hollow rod with holes for a tool in the side. If you give me some dimensions to work with, I'll post a drawing.