You can try to do this by changing the libraries wiring_analog.c and AnalogIO.h
In the website you posted, they show some changes using ADCSRA, this is not implemented in the wiring_analog.c library for Edison so this will not work, you will have to do your own changes in the libraries to make this work.
Another alternative is using MRAA, there is a thread related to this: Re: Edison Arduino board: ADC sampling rate that you may find it helpful.
I found wiring_analog.c and analogio.h but I did not understand how to make changes to it.I want to sample ADC at 8Khz using MRAA. Can some one tell me how to use MRAA for sampling ADC at 8khz.Is it possible with MRAA in the first place?