I concur with what the past respondants have said about simply deflating your tyres and trying to change the tube. If you really want to simulate the true experience, you could try and find that screwdriver you used on your fridge and go at the tyres with it.
In all seriousness, changing the tube in the comfort of your home is a good way to practice for both newbies as well as experienced cyclists. Also, it's a good thing to do anyways as it causes the tyre's bead to "loosen" up a little thereby making it easier to deal with tyre removal and installation when a real flat occurs. Some tyre beads can be a PITA to deal with when they're new and haven't been removed and installed a number of times.