If you can store the AdWords click ID on the server with the IP, you might be able to use your matcher to record the install as a conversion. AdWords should start optimising for installs vs downloads. But if you can carry over to some kind of in app purchase, I’d do that too, using avg value of an install as the install value and then any of the in app purchase values as the conversion values.
Think we filed a patent but it's possible to do this server side to inject a string into a payload area without affecting the integrity of the binary (can't recall how we did it but search patent search for my name at Google)
