Maybe you can use a low distributed capacity UTP or FTP cable and run each line with its own ground (the twisted one). Apart from that, you should reduce dv/dt with one pole passive filter or pi filter (like the ones used for EMI reduction on data lines but with nerarer poles ) on each data line.
In 12 feet, sure you are going to get some common mode noise, that can be reduced making a small loop inside a ferrite toroid.
It is no so expensive to try those solutions, If it doesn't work, I agree with Elcielo's solution.