It is there to reduce galvanic corrosion by insuring a good current path to the sacrificial anodes.. It may be that there is sufficient ground conduction without it that there won't be excessive corrosion but on the other hand, if there isn't you won't know until the damage is done. You don't have to get the exact wire part. You can make up one with a length of stranded wire and a few crimp terminals. It may not hold up forever but it would do the trick.