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 = "

$image2 = "

$image3 = "

$image4 = "

so how to pass these image urls to xupload form ?