I don't recommend that. I used to use buffering salts to lower pH, but the problem is that you increase your total conductivity. In that situation, my fish were OK but did not show any breeding behavior. Once I lowered the overall salt/ion concentration, they started to breed like crazy.
Peat would slightly soften your water by exchanging cations for protons. I'm assuming alder cones work the same way,
@dw1305?
Overall, I believe that lowering conductivity by either cutting your water with rainwater or RO would have a larger affect on the fish that the pH itself. It's not totally clear to me that pH is important. That said, peat, driftwood and alder cones come with the additional benefits of adding humic substances to the water, which are desirable.