Merge? Copy?

I have an XML file similiar to below.  In this example I need the Customer to appear only once, in the real file it may be there once or 20 times.  I need the Sales data do be copied up from any duplicate customer. 

I have thought about doing this using vbscript maybe, but would prefer XSL to do it.  I have looked at merge but that requires loading 2 xml docs in.  I'd also prefer not have a duplicate xml file ... the file will be over 600 megs so loading two would be intensive.   

Is this even possible? 
Any tips would be appreciated.  Thank You. 

<Customers> 
<Customer id="100"> 
<Name></Name> 
<Address></Address> 
<Sales> 
<date>August 1, 2004</date> 
<amount>18</amount> 
</Sales> 
</Customer> 
<Customer id="100"> 
<Name></Name> 
<Address></Address> 
<Sales> 
<date>August 10, 2004</date> 
<amount>22</amount> 
</Sales> 
</Customer> 
</Customers> 

Desired Result: 

<Customers> 
<Customer id="100"> 
<Name></Name> 
<Address></Address> 
<Sales> 
<date>August 1, 2004</date> 
<amount>18</amount> 
</Sales> 
<Sales> 
<date>August 10, 2004</date> 
<amount>22</amount> 
</Sales> 
</Customer> 
</Customers> 

 




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