How to connect a PC application and an Android application together via USB, so they can talk to each other as if they were networked?

Hi, a bit of an odd request, but a very real problem!

TL;DR: I'm looking for a way to get two Unity projects -- one built on Windows PC and the other on an Android tablet -- to communicate with each other via USB, as if by networking. (And no, Unity Remote is not going to work.)

I'm currently working on a two-screen game, with the main game running on Desktop (PC/Mac) and the second screen app, which functions as the player's controller (amongst other things), on a touch device (Android/iOS).

Think sort of like a makeshift Wii U (see e.g. ZombiiU), but on computer and you can use your own phone/tablet to play.

This is achieved through networking: there are two separate Unity projects -- one building to PC and one to Android -- which then communicate with each other by connecting to the same WiFi network through the Unity Networking API.

This all works great and functions perfectly in regular play. However, when taking the game to shows and events, everything breaks down because there's so much WiFi noise from everyone connecting in a small place. We tend to bring our own WiFi dongle, so it's not having access to a signal that's the problem, it's the sheer noise.

So, for the sake of shows such as this (I've another one coming up soon), it'd be great if I could get around this problem.

Ideally, what I'm looking for is a method to get the PC application and Android application talking to each other when they are connected by USB. In an ideal world, I'd be able to use the same networking API (synchronising states and send RPCs).

I don't need a general solution since this is purely for demoing purposes. So if it helps narrow down the solutions, then I really only need to get this working between one Windows machine (I presume it'll be Windows 8.1, but could be 7) and one Android tablet (it'll be a Nexus 7 2012).

I'm working in C# if that makes a difference.

Any help would be greatly appreciated! Thanks in advance =).