First...you will need a plastic dinosaur. You can find these at Walmart for a dollar and larger ones at Toys R Us. I painted my dinosaur with acrylics and sprayed with a finish. I wanted a complimentary color palette for these photos.

Take your Exacto Knife and cut a hole around the top (well...back) of the dinosaur. It is just like carving the top of the pumpkin...except this is plastic.

The hole I created is around 3-4 inches. Thankfully the dinosaurs are already hollow inside.

Then, I put in my plant and gave it water so I could expel some of the water using my sewing needle. I made plenty of holes in the bottom of the dinosaur...you have to apply a lot of force for this part.

Your project should look similar to this in the end after you have added soil and your plant. :D