No, you can add it, the reason for pouring it in on an empty tank is so that the incoming fuel will mix it a bit better, putting it in and driving around will do the same thing. Personally I use the Techron or Valvoline in the gold bottle, both are in the $7 price range, the .99 cents stuff I only use for maintenance between full treatments.
It also helps to clean the throttle body with a spray cleaner if you don't want to pull the throttle body and clean it on the work bench. I just picked up a spray can of gumout that is supposed to be plastic coated safe and used it last week. Got all the carbon off the inside of the throttle body but I still kept it away from the airflow sensor [I'm not that trusting of a label by any means].
Valvoline also makes a gold spray can with a shoot down spray tip which is one handy configuration, I'm just really suprised that the other companies don't have the same down shooting nozzle as the valvoline one.
Seafoam also works well for cleaning the intake and valves, it's a 'pour in and soak' kind that you pour directly into the throttle body till it stalls and then let sit. Warning, it's one smokey startup afterwards though so warn your neighbors

It also won't hurt it to take it out on the hiway and do some wide open throttle runs either, that also gets rid of carbon.