Not sure if i'm late for the discussion, but here go my two 2 cents...
A character of mine once had his Iron Bands of Bilarro at his feet and tried to throw them by
kicking them towards an enemy 20ft away. The DM applied a -4 penalty for "using a weapon in an improvised manner" + -2 penalties for each 10ft (although the iron bands don't specify increments).
I found it a good ruling, and if i was using a really awkward body part or action to do the same (ex.: kick it up to my head and headbutt it, like a football (er... soccer ball?)), i'd agree with an even higher penalty.
Summing up, it all comes down to the limb being used... if the limb is dextrous enough to use, i'd apply the improvised weapon/usage penalty of -4. The penalty can be greater still, if the action is possible but really hard... if not, i'd simply negate the usage altogether (ex.: you can't really expect to be able to attack an armored foe properly with a dagger in your mouth, can you?
**), or apply an "impossible" penalty (ex.: -20 to attack or something like that)...
**This, of course, depends on the size of the mouth and the daggers...
I could probably give a fair penalty to a beholder spitting a dagger made for medium characters, for example...
...hope this helps.