Subfigures or Subcaptions with knitr?

Is it possible to produce subfigures (with associated subcaptions) using knitr? Here is a minimal working example:

\documentclass{article}

\begin{document}

<<echo = FALSE, fig.cap = c("Some numbers.", "Some more numbers."), out.width = "0.5\\textwidth", fig.align = "center">>=

plot(1:10)
plot(30:100)

@

\end{document}

This results in two figures labelled Figure 1 and Figure 2 with captions as defined (respectively). But I want them to be labelled "Figure 1a" and "Figure 1b", as you can do with the subcaption LaTeX package.

I know there is a knitr options "fig.env", but this doesn't solve it (at least not using, for example, "fig.env = 'subfigure'"). There is a similar post here regarding Sweave, but the solution is an inelegant hack: http://texblog.org/2011/12/01/sweave-subfig-controlling-figure-size-and-placement/

knitr (>= v1.5) supports subfigures. You can use the chunk option fig.subcap. Here is a minimal example.

\documentclass{article}
\usepackage{subfig}
\begin{document}

<<fig-sub, fig.cap='two plots', fig.subcap=c('one plot', 'the other one'), out.width='.49\\linewidth'>>=
plot(1:10)
plot(rnorm(10), pch=19)
@

\end{document}