Hi Chris,
Have you got a six point socket or is it the more usual twelve point? The six point, by this I mean it has just a hexagon hole which fits the bolt, is much better for gripping soft-ish alloy caps like an oil drain plug.
Buy a new one, any Honda shop should be able to get one next day or perhaps the day after, then carefully tap the old one around with a hammer and chisel/punch. When using this method, on the underside of an engine, it is all too easy to try to turn the thing the wrong way, especially if you are new to the game. I don't wish to impugn your abilities but are you sure you are in fact un-doing the cap, remember if it under the engine it appears, from the top, to go he other way.
Ned
PS sorry for overlap of six point sockets.