Homemade EEG Circuit Common mode feedback
The problem with the assumption is that EMG signals can be controlled.  It can be a couple orders of magnitude higher level in signal strength and there is no precise way to ensure that the EMG signal can be cancelled due to too many reasons to mention including sensing location and contact pressure.  Even if you had some adaptive AGC the EEG would still be swamped by possible EMG signals and scalp artifact noise from modulating the galvanic DC charge voltage from motion or pressure changes of the electrodes. 

This is why it is done the way it is. 


proper electrode area prep and attachment
Active guarding with CM feedback..
and Right Leg RL ground ( mainly for EKG) or equivalent 0V reference point that is convenient on the body.


Conclusion
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Not feasible.