Add some ripped up cloth like it was a shirt sleeve back before decay set in. I mean, your pirate wasn't buried in the nude, was he? Some fabric scraps make perfect sense. Then, spray paint your rebar a color that matches the arm, zip tie the arm to it, and drape the ripped cloth artistically to cover up where the rebar is most obvious (securing with dabs of glue).
Good luck!
Good luck!