How can my dragons use their tongues to control their fire breathing?
Some background you may or may not skip
I was daydreaming the other day about how tamed dragons whose magic was somehow harnessed as an energy source by humans could be used as a metaphor for nuclear power in modern societies. While considering this, I surprised myself thinking "of course they would need to cut the tongue out of tamed dragons so that dragons can't orient their fire anymore". Don't ask me where I got the notion that dragons need their tongue for that. Still, this got me wondering about what conditions were needed for this thought to be true.
Background you should not skip
In my world, dragons ...
* ... fit the stereotypes defined in this somewhat related question
* ... breathe fire in the way described there except they use magic to conjure the initial flame, inside their mouth. 160
The rest is similar: the liquid fuel is "sprayed" from a reservoir towards the flame, ignites and finally breathing is used to expel the burning fuel. It so happens that this is more efficient than using pure magic to conjure a full stream of fire.(1)
* ... use their tongue to control the direction of the fire they breathe. This constitutes a competitive advantage over their ancestors who had to rotate their heads to do so: (1) the breathing direction can be adjusted to a moving target more rapidly(2) and unpredictably, (2) the head can remain parallel to flight direction for better aerodynamics.
Question
If this is possible, what sort of motion / positioning of their tongue could my dragons use to control the direction of their breathing so that the flame is directed? This might be used in combination with other actions that control breathing, much like whistling. All I need is that the tongue be important enough that if the tongue is cut, dragons loose this ability and fall back on the original approach of turning their heads all the way.
An ideal positive answer would
* explain the mechanism,
* if possible back up its claim with examples in real-world fauna achieving similar purposes,
* not make use of any more magic.
An ideal negative answer would either demonstrate that this is not possible or that a significantly simpler mechanism allows dragons to orient their fire and would lead to the same competitive advantages.
(1): magic consumes mana, which is hard to store and fluctuating. Fuel is a more secure way of storing energy for dragons.
(2): please consider that tongue motion of reptiles is faster that that of humans, and snakes can flick their tongue back and forth at around 15 Hz 160