WE 2500MM Polarity Guard

[poplar1]

I was fearing that John (kka2446) might get the idea that he would have to completely rewire 22 telephones as DMs.

I understand your concern about shorting out the ATA. Other than using a 2-conductor cord, you could also isolate any of the 4 A/A1 leads involved:

(L2 should be a previously unused terminal)

1.  Move yellow line jack lead from L1 to L2
                       OR
2. Move black line jack wire from G to L2
                       OR
3. Move yellow hookswitch wire from G to L2
                       OR
4. Move brown hookswitch wire from L1 to L2
                       OR
Tape and Store any of the 4 leads.