The 550ex does not have a PC socket.
You are going to need something like this:
But with a PC on the other end instead of that pocketwizard miniplug. Call paramount cords and tell them what you want, they will sell you one.
Or, buy a standard canon TTL off-camera cord. It should sync just fine in manual mode with the R-D1. Although I would test this at the store before I bought one.