If the wire passes near bulkheads, glue in some supports. Heck, if it's just near anything wood, glue in supports.

Almost no weight added and you get the same result.

You can cut short pieces of pushrod tubing (which is made for this job) and slip 'em on the rod. Slide 'em to where the bulkheads (whatever) are and glue scrap balsa to fit. Bingo.......

Two or three are enough for fuselage length rods.

Can't reach down inside the fuselage? Are there lightening holes in the fuselage bottom/sides? They're perfect semi-perminent hatches. Cut out the covering and worth through the hole/hatch. Iron on a patch of the same color covering after the brace is in place.