#  also untested
use Path::Tiny qw /path/;
use FindBin qw /$Bin/;

my $exe_name = 'some_exe';
my $exe_path;
if ($ENV{PAR_0}) {  #  running under PAR - look for the unpacked exe file
    $exe_path = path ($ENV{PAR_TEMP}, 'inc', $exe_name)->stringify;
}
else {  #  not running under par, assume file is adjacent
    $exe_path = path( $Bin, $exe_name )->stringify;
}

#  set the env var
$ENV{GLOBAL_PAR_TEMP} = 'C:\some\path';

#  now run it
#  maybe use exec or wrap it in Capture::Tiny::capture
system $exe_path, @ARGV;