Modify the display ratio after the slides have been rendered

[yihui]

I know we can specify the ratio in remark.create({ ratio: ... }), and I wonder if it is possible to change it after the slides have been rendered, so I can adapt the slides with different screens. It will be even better if there is a keyboard shortcut to change the ratio on the fly, e.g. I have used ioslides before and you can press w to toggle between 4:3 and 16:9: http://slides.yihui.name/2014-JSM-knitr-Yihui-Xie.html