sub handler {
    my $r   = shift;

    my( $id, $step ) = (split( /\//, $r->path_info ))[1,2];

    if( ! $step ) {
        $step = "step_one";

        # Seems to have no bearing on $ENV{REQUEST_URI}
        my $ruri = $r->uri . "/" . $step;
        $r->uri( $ruri );
        $r->subprocess_env( REQUEST_URI => $ruri );
        $ENV{REQUEST_URI} = $ruri;

        # Modify path_info
        my $pinfo = $r->path_info . "/" . $step;
        $r->path_info( $pinfo );
        $r->subprocess_env( PATH_INFO => $pinfo );
        $ENV{PATH_INFO} = $pinfo;
    }
    ....