Fire and Ice
For the first method, head up to the next floor and stack into both the small kid with the ice bucket and the fireman.
Take these two dolls down to where Sly is and first use the Fireman to spray water on him.
Next, use the kid with the ice bucket to freeze the water, thereby freezing Sly, making him fearful of catching a cold.

Pigeon Bisque

Head up to the second floor and stack into the doll with the soup bowl on his head.
Continue going upwards until you reach a room with a pigeon. Head inside and the pigeon will automatically land on your head.
With the nasty pigeon flavored soup on your head, return to Sly, who is so hungry he will immediately slurp up the soup as soon as you get close.

Sneezing Wild Fire

Next up, head back to the pen you unlocked and look for a doll with a pepper shaker on her head.
Lead the pepper shaker doll back to Sly and use her ability to make Sly sneeze.

Snot Soup

This one is similar to the previous method. Once again, stack into the soup doll, but this time get the sick doll to sneeze on you.
Bring the sickness ridden soup back down to Sly, who will eat it and immediately start to feel sick.