r - how to achieve a hand-drawn pencil fill in ggplot2?

I came across this great blog post on visualizations: http://www.darkhorseanalytics.com/blog/visualizing-distributions-3
It includes a set of plots with an aesthetic that looks like hand-drawn pencil. Is there a way to get a textured fill like this in R, preferably using ggplot2? I know about the hand-drawn fonts and lines available in the xkcd package, but I'm particularly interested in getting the hand-drawn fill effect, as shown in the following histogram (taken from the darkhorseanalytics link posted above), which isn't available in the xkcd package.

Any ideas on how to create something like that in R?

To be clear, I'm looking for ideas about how to generate a hand-drawn fill effect, similar to the hand-drawn effect for lines that has been the subject of very productive brainstorming on this site. Fill effects are not easy to implement in ggplot2, but not impossible. Jittering a diagonal fill lines effect may be a reasonable place to start. Ben also mentioned annotation_raster() which would be another reasonable approach.

I know fill textures are not currently a priority for the ggplot2 development team, and they're difficult to implement for a number of reasons. That doesn't mean that they wouldn't be useful to have, or that we can't try to figure something out. :)