Message mapping issue

Hello,

I got the following structure:

<ITEM_TAB>
  <item>
    <number>1</number>
  </item>
  <item>
    <number>2</number>
  </item>
</ITEM_TAB>
<ITEM_EXT>
  <item>
    <number>1</number>
    <tax_name>TAX 1 FOR ITEM 1</tax_name>
  </item>
  <item>
    <number>1</number>
    <tax_name>TAX 2 FOR ITEM 1</tax_name>
  </item>
  <item>
    <number>2</number>
    <tax_name>TAX 1 FOR ITEM 2</tax_name>
  </item>
  <item>
    <number>2</number>
    <tax_name>TAX 2 FOR ITEM 2</tax_name>
  </item>
</ITEM_EXT>

And I need to get the following XML:

<ITEM_OUT>
  <item>
    <number>1</number>
    <tax_name1>TAX 1 FOR ITEM 1</tax_name1>
    <tax_name2>TAX 2 FOR ITEM 1</tax_name2>
 <item>
 <item>
    <number>2</number>
    <tax_name1>TAX 1 FOR ITEM 2</tax_name1>
    <tax_name2>TAX 2 FOR ITEM 2</tax_name2>
 <item>
</ITEM_OUT>

It's possible to do this using message mapping ? If not what you suggest me?

Regards.