With the recently-introduced download cap in Kuwait, I had to figure out a different method of downloading my files. Now I use my Viva 3G mifi card as a second internet line, in addition to the home DSL (at the same time).
I looked everywhere for a reasonably easy way to download from both sources without buying additional hardware or messing with complicates configuration files and/or scripts. I simply use a virtual machine and forward to it the entire 3G card connection.
On your Ubuntu (or windows) computer, set up a virtual Ubuntu machine with bare minimum software and select the 3G as the network source. Now share one of the computer folders with the virtual machine and start downloading on both connections simultaneously.
If you're having any problems with this method let me know in the comments section below this post.