Using an undocumented preference value, you can use the undocumented XSIUtils.DisplayHtmlHelp method to open compiled help files. To find the undocumented preference value, I had to go into the Softimage source and find the implementation of DisplayHtmlHelp().

Prior to 2012, DisplayHtmlHelp worked with CHM files, since the Softimage help itself was compiled. But as of 2012, DisplayHtmlHelp now works with HTML files by default.

// Set the helplocationtype to CHM
var tmp = Preferences.GetPreferenceValue( "General.helplocationtype" );
Preferences.SetPreferenceValue( "General.helplocationtype", 3 );

// Open a specific topic in a compiled help file
var s = "C:\\Program Files\\7-Zip\\7-zip.chm::/fm/plugins/7-zip/options.htm";
XSIUtils.DisplayHtmlHelp( s );

// IMPORTANT: Restore pref after
Preferences.SetPreferenceValue( "General.helplocationtype", tmp );