If a guy is going to be a space pirate, then the OP's method is the most sound. However, it's still a strongarm robbery no matter how you slice it. But since it's a game and allowed under the current scheme of things, such is life.
But even though it's a "crime" it's not a "reportable" one using the current setting of "REPORT CRIMES AGAINST ME" as it won't pass the filter test. As it is now, interdicting a clean vessel is not a crime, a strange fact to me. And since the exchange between an aggressor (OP, in this case) and the other player is one of "hand over some of your stuff or I kill you" type, it's a robbery under the threat of violence on its face. As such, my idea earlier is sound and contradictions to it claiming the "REPORT CRIMES AGAINST ME" function covers it are without merit.
I think if I were to play on the Open server, I'd keep X tonnes of something valuable for negotiating purposes, but the few times I've been killed in the Open the other side has been interested in thrill killing only and not for any discernible profit, motive, preferring to do "crime" just for the fun of it.