Correct, you need to bring the Regis to the statue to activate it. To obtain the Regis in Pokemon Platinum, you need to migrate them over using Pal Park, or from an Event that has already passed. They cannot be found in Pokemon Platinum.
If you have a regular DS, you can use the Migrate system if you caught the Regis in Ruby, Sapphire, or Emerald to transfer them over. If you cant, then you can't get Regiggigas at all.