How can one set javadoc options in a wrapper of the standard doclet?

Question

The UMLGraph doclet UmlGraphDoc first runs the standard Java doclet with code like the following:

public static boolean start(RootDoc root) {
    com.sun.tools.doclets.standard.Standard.start(root);

and then modifies the result to add UML class diagrams.

The UMLGraph doclets introduce a number of custom tags, such as @depend and @has. Custom tags can be specified using the Taglet interface and passed to javadoc with the -taglet and -tagletpath options. My question is: how can these options can be specified to the standard doclet when it is invoked from another doclet?

Here are some things I have explored:

• The javadoc Taglet manager offers an addCustomTag method, but this is not a public API.
• Implementing the com.sun.tools.doclets.Configuration class could allow the specification of options. There are hints in an old implementation I've found that this could work, but this, again, does not seem to be part of the javadoc public API.
• Subclassing (rather than calling) the standard doclet. The provided documentation is outdated and contains dead links. Not very reassuring.
• Running the standard doclet programmatically, rather than extending it from another doclet. It is not clear how this can work from another doclet.