How to supersample TTF text of UI in 3D graphics scene?

Unity 4.6 offers the ability to create TTF text in the UI canvas.

However, suppose I want to capture the 3D graphics scene at a supersample screenshot mode of 2 times supersampling. For example, for a viewport resolution of 640x360 I would be able to capture a screenshot of resolution 1280x720. I would need to scale down the TTF text by a factor of 2 for the 2D text to appear in the viewport at the desired size in the final screenshot.

The 3D graphics scene scales up correctly in the final screenshot. No noticeable artifacts.

However, the problem is that the 2D text appears pixelated in the final screenshot. What do I need to do so that the 2D text appears correct and not as though a 1x1 pixel has been sampled and mapped to 2x2 pixels? For example, if the original TTF text has a font size of 36 in the desired 1280x720 final screenshot, I had to change the font size to half i.e. 18 in the 640x360 viewport.