There is a very basic but simple solution to this, with a nice transition between the 2 for free.
You can use SET CAMERA TO FOLLOW for both views. When teh user toggles between the 2 you simply change the settings - height, distance and smooth.
For 3rd person, the height will be greater, so you can see over the player. Distance will be something suitable and smooth somewhere around 20 to 50 depending on teh effect you want.
For first person, set the distance to a very small number (not zero, or the POINT CAMERA details will also need to be updated). Height will probably be 0, and smooth is reduced to almost 0. When first person is selected, hide the player object.
I used this in my Snake Compo entry and it worked very well.