Follow this link to the Brick Correct page and add the feature.
Select either the "My Brick" or the "Brick Correct" feature in the custom feature dropdown and specify the type of brick you would like to make.
Move back to your assembly tab and import your new bricks. You can change the orientation or position of your bricks by clicking on them and using the triad manipulator tool
Create and import as many custom bricks as you need to assemble your your own custom duck!
Once again use either planer or fastened mates to connect them.