Copy this file into your Perl core lib directory:

package CORE::Relocatable;

sub import {
    return
        if $^O eq 'MSWin32' # or whatever check you deem necessary

    if (not $ENV{PORTABLE_XL_PERL}) {
        require FindBin;
        local $ENV{PORTABLE_XL_PERL} = 1;
        local $ENV{PERL5LIB} = '';
        local $ENV{PERLLIB} = '';
        exec("$FindBin::Bin/perl", $0, @ARGV);
    }
}

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... and have all your scripts

use CORE::Relocatable;
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Duh - I don't know whether a relocated Perl on Unix will know where its site/lib directory is, so this might still be a nonstarter :-(