It seems to me that loading all of PG is probably overkill if you're just trying to display HTML with formulas. It's pretty easy to just include the jsMath Javascript libraries in the HTML file and thus get the equation formatting that way. See <http://www.math.union.edu/~dpvc/jsMath/authors/basics.html>: The easy/load.js file is available on your WeBWorK server at the URL <http://your.server.here/webwork2_files/jsMath/easy/load.js>.
If your WeBWorK installation is new enough to have MathJax, you can use that similarly; see <http://www.mathjax.org/docs/1.1/start.html> (and the MathJax.js file is at <http://your.server.here/webwork2_files/mathjax/MathJax.js>.
Hopefully that's useful,
Gavin