Detecting edges on mobile on flat shapes?

I am developing game for mobile, so i keep texture sizes minimal. My idea is to make menu out of 3d shapes, without using any texture (at least for non text boxes circles etc).
I know that fresnel can detect edges on 3d objects, but going from flat shape to 3d object will at least triple polycount for menu. Using UV layout mask gets me back to beginning, its just better to not bother with shapes and use images instead of shapes. I am also not sure if postprocess material with scene depth is not too heavy for mobile.

So I need to detect, and have glowing edges of flat shapes without use of any textures. My whole interface is rendered in 3d and attached to camera. Probably HUD or UMG would be much easier but that means going back to textures. Also the challenge, and only one problem is that glowing edge material.

I am going for material that looks like this big circle in middle.

Any suggestions?