Update 22-09-16: DJI have released an official X5 and X5R Z-Axis for the Osmo – http://store.dji.com/product/osmo-pro-raw-z-axis
Facebook User Cell Gunlaw has modified his DJI Osmo Z-Axis with an upgraded spring to take the weight of the X5 camera. To achieve this he added a 70x15x1.8mm compression spring to replace the one the Z-Axis comes with. He states that doing this renders the Z-Axis useless for use with an X3 as the weight needed to make it perform is not there with an X3.
Another concern is the weight being placed on the handle. I think it will be OK as you do have the extra support from the screw in to the side of the Osmo Handle but it’s still a risk you would be taking.
He shared a clip showing it in action – https://www.dropbox.com/s/8w0gzr5ut900hxz/DJI_0081.MOV?dl=0