Idoc attachments

I have to send PO Cretaion IDoc from R/3 from third party system using XI as middle ware. The requirement is not only send the PO IDoc but with an attachment (which is *.doc, *.jpg etc document). The attachments are stored in a database with will be attached to PO while creating the PO.

Our approach to send the IDoc along with attachment to XI is as fillows:

1. Extend the IDoc XML with a field containing the binary data

2. The binary data must be encoded using an algorithm like BASE64

3. In the IDOC creation user exit in R/3 read the binary data, encode it to BASE64 and add to the element within the Idoc XML

4. Map the fields in the IDoc to the receiving WSDL format.

Is there any other easy way to achieve this?