Right Driven Leg for two or more channels


I am developing a biopotential acquisition system (EMG/ECG) and I intend to have at least 2 channels.

I found some information about RDL for one channel and I was  able to implement it. But for two or more channels I did not find any info.

I do not want to have an electrode of DRL for each channel. What should I do to use only one electrode of DRL for all channels? Should I sum the DRLs output and then calculate the mean?

Thank you in advance.