can you get power to it? even a little portable gen? it will stall it a few times due to inrush filling up the capacitors in the machine, but then you can run it/lower it.
OR
Try spinning with a wrench, you will have to overcome the integrated servo break though. I cannot imagine its that powerful of a break. its a simple permanent magnet pulling a clutch plate together. when voltage is applied a counter field is created and overcomes the magnet to disengage the break. (when you hit the E-stop, the click you hear is the controller turning off the power to the magnetic coil and the permanent magnet snapping the clutch/break down)
OR
you could also put voltage to the break on the pin out plug. varying the voltage will change the amount of "release" on the break, all the way off and it will freewheel and drop the head. lower voltage will allow the break to drag a varying amount. of course this is (electrically) at your own risk!
OR
place a jack under the spindle. crawl on to the machine and dismantle the tip end of the servo motor.
1.carefully remove the encoder. (I cannot stress this enough)
2. remove the top cap, the break will be mounted in it, likely keyed to the shaft.
I've done this with my lathe when the break coil failed and my x axis would overheat when working because the break was dragging.
its pretty simple, but for someone unfamiliar with electric servos/motors can be scary I guess. I've worked on hundreds of them, so no F's anymore.
best of luck!