I would have another breaker put in only for your grows. Of course you would need to break it down if you have to have someone come in to do that. 20 amp, by the way. Then you could hook up all the light you want. Also, check the sockets in and around your grow, depending on how old your house is, you may find that there's another outlet in the room on another breaker. Or, you could find out that the whole second floor (or basement) is on it.
What I used with my cfl's was this
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I took the same splitters you have, to make it four bulbs in one. You need to buy an extention to get 'em to screw into it. Then cut the reflector on opposite sides, almost in half, and bend it up so that you can get all the bulbs under it. Those 65w might stick out a little bit, but some light reflected down is better than none.