SWIG: How to wrap std::string& (std::string passed by reference)

I am using SWIG to access C++ code from Java.

What is the easiest way to expose a std::string parameter passed by non-const reference?

I have primitives passed by reference exposed as Java arrays, thanks to typemaps.i, and const std::string&s exposed as java.lang.String, thanks to std_string.i. But a non-const std::string& is exposed as opaque pointer type SWIGTYPE_p_std__string.

Current:

// C++ method                     -> // Java wrapper of C++ method
void foo( int & i )               -> public void foo( int[] i );    // OK
void bar( const std::string & s ) -> public void bar( String s );   // OK
void baz( std::string & s )       -> public void baz( SWIGTYPE_p_std__string s ); // :(

Desired:

void foo( int & i )               -> public void foo( int[] i );    // OK
void bar( const std::string & s ) -> public void bar( String s );   // OK
void baz( std::string & s )       -> public void baz( String[] s ); // OK

UPDATE: I found a solution, described below. However, it took more effort than a few seconds. I'm still interested in hearing about easy approaches.