After 3 days of work I found a solution. Not elegant nor practical, but it works. After setting the variable export MACOSX_DEPLOYMENT_TARGET=10.11 (with the desired OS version), I reinstalled Perl with Perlbrew. In this way the MACOSX_DEPLOYMENT_TARGET was set inside the Perl installation too (visible through perl -V. For all the rest, I proceeded as usual. The final executable created with pp finally had:

Load command 9
      cmd LC_VERSION_MIN_MACOSX
  cmdsize 16
  version 10.11
      sdk 10.13
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