There is not a simple documented way to do this efficiently as far as I know. However, one way to approach it is to use tools in Wolfram workbench. I have not use these so I cannot comment on them. There is a fair amount of complexity and setting things up for the documentation center. However I and some others in the past have a reverse engineered some of this and some information on this appears in the Documentation Center Notes notebook at the following link:

http://www.scientificarts.com/worklife/notebooks/index.html

Note that this was written several versions of Mathematica ago, so there maybe details that are no longer quite correct. I have not checked it recently. However it will give you a sense of what the internal mechanics are.

You will also want to take a look at the documentation for Wolfram workbench to see how it can be used with its tools to create documentation center pages.