how to use the xuploadform with external url?

Hi,I need to share the uploaded data from one portal to another portal.

e.g upload to site A then share/save the same photo so site B

I’m not using the XuploadForm extension in site A, but in site B the XuploadForm is being used.

how to feed the xuploadform of the site B via backend, if I can only pass external URLs like e.g

$image1 = "http://www.blablalab.com/aahahaha/1.jpg

$image2 = "http://www.qfqdfqwefqwef.com/ahahahah/2.jpg

$image3 = "http://www.2342343.com/ahahahah/3.jpg

$image4 = "http://www.asdf3erqwe.com/dfasdfadsfsd/4.jpg

so how to pass these image urls to xupload form ?