I had a bass delivered by DHL from Portugal - inside two cardboard boxes (heavy duty ones) and packed with bubble wrap and loads of brown paper. It was so well sealed it took me more than half an hour to get the package open. But inside the guitar was perfect. So I would suggest filling the hard case with bubble wrap and then putting the hard case inside a strong cardboard box, also with all the voids packed with bubble wrap, and the whole thing covered in parcel tape. Any courier will chuck it about, but if it is seriously well packaged it'll be fine.
Don't forget to insure it!