nvd3 scatterPlot with rCharts in R: Vary size of points?-open source projects novus/nvd3

I’ve been playing with rCharts and nvd3 for a bit of time now. Now I’m in a situation where I need a bubble chart, or at least a scatterplot where the size of the dots is dependent on a variable in the data. From this example, it seems possible. The example on scatter charts in rCharts is:

library(rCharts)
p1