Can it be done?
Instead of giving out activation codes for episodes or seasons (an idea that probably wouldn't work because of the potential for abuse), what if we could permanently link our entire account here on TTG with our account on Steam? I believe it would prevent someone from selling activation codes to the highest bidder if their activation code is only compatible with one Steam account. Perhaps you wouldn't even need activation codes? Hypothetically, if we were to pass our Steam account info to TTG, purchases made here could be communicated to Valve and then added to Steam, right? Of course, I don't think Valve would agree to do this unless it was profitable for them, but honestly, I don't mind paying them a few extra bucks for this service. That's still better than buying it twice.
Also, I don't know whether or not this would lead to a communications nightmare, but I figured it's an idea a that's little different and, as far as I know, hasn't been thrown out there yet.