I'm not sure about ColdFusion, but try adding the string "?blob=base64" to the URL for the web service call (works in Java and .Net).
The LiveCycle web services can accept binary data as base64, MIME and DIME encoding as well as passing a URL to the file (rather than the file itself). You specify the type you want by adding the blob parameter onto the web service target URL.
You should then be able to send the data using the BLOB.setBinaryData() and get it out using the BLOB.getBinaryData() methods.