Translucent ggplot2 background for powerpoint

The following parameters will render a translucent ggplot. When pasted into powerpoint, the background will not appear, leaving only the powerpoint template.

ggplot() + 
  theme_minimal() +
  theme(panel.grid = element_blank())

Unfortunately, this doesn’t work with theme_bw() or theme_classic().

Bo\(^2\)m =)