[Q] Tethering issue

Apologies if this has been asked before, but I've searched and couldn't find anything that matches what I'm after.
I have a GNex running custom 4.2.2 and Windows 7 x64.

I want to be able to access my phone from my PC. To do this, I installed AirDroid. All good so far.

Issue 1: Using WiFi to access the phone, it doesn't do anything when the screen is off/the device is locked. Annoying.
Issue 2: Using USB tethering, it works fine when the screen is off, but kills my PC's internet access. Also annoying.

I would like to use USB tethering if possible, but I only want to be able to access my phone via AirDroid, not use it for internet (my PC has a much better wired connection already).

More on issue 2: Windows says the DNS server is unavailable when I troubleshoot. The moment I plug in my phone and the NDIS-thingy connection is formed, I lose internet access via my normal connection. It goes back to normal as soon as I unplug it. I've tried changing the priority of the network devices, but to no avail.

Any help appreciated.