So, not sure if this works.
If someone could investigate we could all benefit from it.
It's going to require that we all play together if we want the parks, assuming this method works.

Step 1. Save a clip at the park you want to download. (Custom skate park that a friend has)
Step 2. Go offline.
Step 3.Save that clip multiple times until the message pops up and says your skate reel is full.
Step 4. When the option pops up saying "continue without saving" or "skate.reel", simply press the back button/ B for Xbox ○ for PS3.
Step 5. It should bring you to the park that you duplicated the clips of. (You may spawn outside of the park. If so, press the edit park to spawn back in.)
Step 6. Save and download.

Reference:
https://www.youtube.com/watch?v=7rwGYN8vwGE