Solved: Thanks jdporter and choroba and corion (for help in CB).

By declaring a package name I can avoid the namespace collision: 

  if ( $compressor ) {
    my $namespace = 'My::' . $compressor;
    if ( ! eval "package $namespace; use $compressor; 1;" ) {
      die "Could not load $compressor - $@";
    } else {
      ...
    }
  }

[download]
And then I can access the imported subs through my namespace by forming the full sub name into a string and by turning off strict refs: 
  } else {
    my $compress   = "My::$compressor\::compress";

    no strict 'refs';
    my $compressed = &$compress( $raw ); 
    use strict 'refs';
  }

[download]

The way forward always starts with a minimal test.

In reply to Re^2: Resolving 'prototype mismatch' warning by 1nickt
in thread Resolving 'prototype mismatch' warning by 1nickt

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