No sound from iPhone speakers when connected to a dock with line out

Question

I've bought a (very cheap) dock for my iPhone 4, the dock has a line out jack on the back.
I have noticed that when the phone is in the dock, the sound comes out only from the line out and not from the internal speakers.
This makes impossible to use any third party alarm application because no sound plays without connecting some external speaker. Only the ringtones play, so the default Clock app works and plays the alarm sound.
Is there any software option to force the iPhone to use the internal speakers also when connected to a dock with a line out?

Answer 1

No, it is a feature. I'm not sure if there is a fix for jailbreaked iphones, but there isn't such an option.

Answer 2

When docked your the doc connector, pin 21 is connected to a resistor to tell the phone what type of dock you are connected to. There is now way to override this without changing the hardware in your dock. Pinout Reference

Answer 3

This question was also asked on another forum. Someone there suggested a trick to opening up the dock and cutting a line, in it.