virtual shipment: can download directory reside in an external site?

[ruisdb]

Hello.
I am reaching my site space limit.
I've thought in using dropbox as an "external disk".
I've installed the dropbox manager component and i can sync perfectly the files in dropbox and in the site.
The problems begin when i try to configure the safe path: it insists that it must be inside my domain. I am using /home/xyz/vmfiles
If i try to place the dropbox link in the safe path, error warnings start coming in...
I don't have no problems in keeping the /invoices directory in there...
But is there something that can help the "shipment for virtual products" plug-in to link to the files placed in dropbox.com/whatever?

I am using joomla 2.5.19
php 5.3.28
virtuemart 2.0.26d
and have no problems using the plug-in.
I want the change because a am in need for more space to the downloadable products.