I figured out grab a version of WkHTMLtoPDF on my server using my own answer:
add-apt-repository ppa:pov/wkhtmltopdf
But this is giving me version 0.12.1 and as of Jan. 19, 2015 version 0.12.2.1 has been released. How do you specifically indicate the version of the repository you want to add-apt-repository?