I would be surprised if you could get the source code, but someone has implemented another Google Home app to deal with this type of issue. You should be able to find a link in the community...
I agree Lewis. I have extended the app to support the AVR device type and it works fantastic, much better than the previous solution I had which included a harmony hub!
I'm super busy ATM, however I will contribute the code back. I'm going to move all my inovelli switches over to the community GH app shortly!