I would totally just park in DTD, how they would know (or give a crap) that you stopped in DLR is beyond me. I have done this several times, and stayed within the free parking parameter and it was cool.
Worse case scenario, don't get your parking validated, bring some sucs and other RSI meds, and just take out the parking attendant.
We do that all the time. I usually go to Goofys kitchen to validate and its 5hrs free. We usually only stay for 3-4 hrs anyways. But ifyou are staying the whole day its not worth it. Theres no rule that you can't park there if you are going to DL or DCA. Its jsut not recommended since most people stay longer than 3 hrs and it cost like $6 an hr and max is $36 a day.
We got to the Mickey & Friends Parking Structure last night around 5:30, and there were no parking attendants at the toll booths.
The point isn't to get free parking, it's to avoid the tram and be dropped off right inside of Tomorrowland. I have parking on my AP, but I will park in Downtown Disney whenever I will be there for a couple hours.