r - How do I preserve transparency in ggplot2?

Question

I love the plots that ggplot generates. However, it is still somewhat cumbersome to get publication quality plots directly. I usually have to do some post processing in Illustrator (i.e. changing fonts, numbering figures etc). While I could save as tiff or png, eps is best for manipulating figures in Illustrator (I can ungroup objects, move the legend/text etc).

When I save a ggplot object with some transparency (either in points or a smoother) I get this error:

Warning message:
In grid.Call.graphics("L_points", x$x, x$y, x$pch, x$size) :
  semi-transparency is not supported on this device: reported only once per page

Is there a workaround?

Answer 1

This works:

ggsave("filename.eps", device=cairo_ps)