How to create a new XML::DOM::Document root in perl

I'm trying to modify some code that was using LibXML to use XML::DOM instead as LibXML isn't available on my fatcow server. My question is: How can I set the root document of a XML::DOM::Document? There is no setDocumentElement method in XML::DOM::Document.

Here is the code in question (from XML2JSON.pm), with the line I'm trying to figure out how to replace marked with **********:

=head2 obj2dom

Takes a perl data structure as input. (Must be a hashref.)
Returns an XML::DOM::Document object.    #JMO

This method expects the object to be in the same format as
would be returned by the xml2obj method.

=cut

sub obj2dom
{
    my ( $Self, $Obj ) = @_;

    croak "Object must be a hashref" unless ref($Obj) eq 'HASH';

    my $Version  = $Obj->{ $Self->{attribute_prefix} . 'version' }  || $Obj->{'version'}  || '1.0';
    my $Encoding = $Obj->{ $Self->{attribute_prefix} . 'encoding' } || $Obj->{'encoding'} || 'UTF-8';

    #my $Dom = $XMLPARSER->createDocument( $Version, $Encoding ); #JMO
    my $Dom = XML::DOM::Document->new();                          #JMO
    $Dom->setXMLDecl($Dom->createXMLDecl($Version, $Encoding));   #JMO

    my $GotRoot = 0;

     #delete @$Obj{ grep { /^$Self->{attribute_prefix}/ } keys %$Obj };

    foreach my $Key ( keys %$Obj )
    {
        $Obj->{$Key} = "" unless defined($Obj->{$Key});

        my $RefType = ref( $Obj->{$Key} );
        warn "Value ref type for $Key is: $RefType (value seems to be $Obj->{$Key})" if $Self->{debug};

        my $Name = $Key;

        # replace a "$" in the name with a ":"
        $Name =~ s/([^^])\$/$1\:/;

        if ( $RefType eq 'HASH' )
        {
            warn "Creating root element: $Name" if $Self->{debug};

            croak "You may only have one root element: $Key" if $GotRoot;
            $GotRoot = 1;

            my $Root = $Dom->createElement($Name);
            $Dom->setDocumentElement($Root);        # **********

            $Self->_process_element_hash( $Dom, $Root, $Obj->{$Key} );
        }
        elsif ( $RefType eq 'ARRAY' )
        {
            croak "You cant have an array of root nodes: $Key";
        }
        elsif ( !$RefType )
        {       
            if ( $Obj->{$Key} ne '' )
            {
                unless ($GotRoot)
                {
                    my $Root;
                    eval { $Root = $Dom->createElement($Name) };
                    if ( $@ ) {
                        die "Problem creating root element $Name: $@";
                    }
                    $Dom->setDocumentElement($Root);        # **********
                    $Root->appendText( $Obj->{$Key} );
                    $GotRoot = 1;
                }
            }
            else
            {
              croak "Invalid data for key: $Key";
            }
        }
        else
        {
            warn "unknown reference: $RefType";
        }
    }

    return $Dom;
}

Thanks in advance for your help!!