We currently don't use native controls. The form elements are CSS styled and look the same on all platforms.

But it would probably be possible to get the toolkit to render the control to a texture or something and move on.

Not really, unfortunately. Native toolkits aren't designed for this. As an example, I looked into using HIToolbox (the API Apple uses) for this on the Mac, but it was so obviously unsupported and likely to break at any time that I quickly decided against it.