Instructions
Start your game. Go into the Creature Creator.
Create your creature's spine, making sure that it's located roughly at the height at which you want it to be flying or floating.
Add a pair of legs to the low end of the spine and merge the legs so that they become a single limb.
Add an accessory part to the bottom end of the leg. This is usually a fin or a small tail, but you can use whatever you like, so long as you keep it small. Position your leg so that the bottom end is pointing toward the ground.
Attach a grasper hand part to the end of the leg. Click on the node at the bottom of the leg and scroll the mouse wheel up to make the leg end grow. This will cause the additional accessory you attached to the leg to float away from the end of the leg.
Shrink the grasper. The end of the leg will automatically adjust to fit the grasper, but it won't affect the distance between the end of the leg and the accessory.
Create the rest of your creature, customizing it however you like. The creature will fly/float when you are done, with the accessory part dragging along the ground unseen.