Although you could just tie it all together, braid and center core, and use it as one conductor. Should work fine.

The idea is either multiple conductors or a wide strap. This is to overcome the "skin effect" of RF currents. (RF current tends to travel on the outer thin layer of any conductor, so a wide path or multiple paths provide the most "skin." )

The one thing NOT to use is a single wire.

Strand cable, braid, wide strap all work well. If you can't find anything else... strip several tinned lamp cords and twist it all together. (the bigger the bundle--the more conductors, the better)