Optimizing Drawcall of UGUI for mobile

I am stuck on reducing draw call under 100 for Gear VR,
and I found each GUI element consume 1 drawcall is killing performance.
When I step in to the frame debug it say it cant batch anything.Reason is objects have different materialpropertyblock set.
I make sure they use single material and in sprite packer they are in one atlas.
I am using unity3d 5.6.2p1.

In worst case I can make a 3D object with single UV and a atlas contain all UI.
But doing such will make things complex when I need to update the UI.