IlovemyPhillip, you do not need any extra equipment to adjust a "head set". When he drives from behind and rounds the head will come to the "head set" naturally.
And don't expect it to happen in day, week, or even a month, because until he'll build all those muscles (which is a gradual process) he won't be able to stay in it. I going to suggest what I suggest most of the time in such situation - take some lessons with the good dressage trainer (at least for couple months). Trainer will help you to get an idea of how to deal with the problem (and I'm talking from the personal experience here - I had exactly same problem with my paint - head in air, run-run-run).
You can also do some search in "English Riding" and "Dressage" sections. The problem of the "nice head set" was discussed there number of times with the great advices on how to "deal" with it. But again, any advice on web won't substitute a live trainer who can see what's done wrong.
P.S. You have to know how to use side reins if you want to use them. I'd suggest not to unless you are experienced with them.