One way I've seen this done is from the Microsoft Add in - 'Web Viewer'
I just tested this by inserting an instance into a slide, and giving it the link
plotly.com/r/getting-started/#getting-started-with-plotly-for-r.
There may be another way with http://skp.mvps.org/liveweb.htm
but I don't have time to test it.
Here is a method for exporting as html
library(plotly)
library(htmlwidgets)
fig <- plot_ly(midwest, x = ~percollege, color = ~state, type = "box")
fig
widg <- plotly::as_widget(fig)
htmlwidgets::saveWidget(widg,"mywidge.html")