Force to use 3G and WiFi is on? Can I force android through settings to use 3G for all downloads when both WiFi and 3G are on?

The main reason why I am trying to achieve this is that I want to use WiFi only as a mean to connect to ADB (without use of USB).

I have Nexus 4 phone which runs Cyanogenmod 10.
The Short Answer

Nope, not possible, or at least compicated &amp; tedious, because Android defaults to WiFi since it's generally faster, more reliable and has no data cap

However

You may want to look into this app. While it requeires a rooted device, it allows you to leverage on both your WiFi &amp; 3G to download at the same time.

The Long Answer

As t0mm13b has suggested (and I eagerly defer to him), if you're really serious about this and have the necessary expertise, you can 


  modify the source code to remove the mutually exclusive flip/flop and also at the RIL layer


Unfortunately, I'm not qualified enough to do more than point you in the direction of the Android Developer Page if you decide to go down this route.