Millers do a running in oil called CRO. Its a very good running in oil and offers good protection too. Ive known turbo engines be run in on dynos including a power run to bed the rings in.
As mentioned already dont be too gentle with it as the bores can glaze.
I would drive it normally as if going for a nice drive out and occasional full throttle bursts in High gears with the rpm starting at about 2500 rpm. This will put more pressure in the cylinders without over revving. Similarly lifting off and coasting down helps the rings seal in the ring grooves too. Basically varying the throttle is a good thing and sustained engine speed is not so good.
If using CRO I would leave it in for 500 mils and then go for the oil of your choice and thats it
I dont see the need to keep going steady for 1000 miles. The factory never did, plus the oils are superior now