To be able to exchange data between your Nexus 7 and your KUbuntu Box, you need to install the kio-mtp package, from the experiental ppa.
To install kio-mtp, follow this steps:
Add the PPA:
$ sudo add-apt-repository ppa:kubuntu-ppa/experimental
Update the syste:
$ sudo apt-get update
Install the software:
$ sudo apt-get install kio-mtp
The difficult part ended. When you plugin your Nexus the OS will recognize it and display an connect option. After you turn on your device, it will show as “Portable Media Player” and next you can drag and drop your files on it.
I have tested this on KUbuntu 12.10 and KUbuntu 12.04 and it worked fine for me.