Sad that perl2exe breaks $^X. They probably consider this a "feature". You could try asking the OS more directly:

use Win32::API ();

sub GetPerlExePath {
    my $f= 'GetModuleFileName';
    my $m= Win32::API->new( 'kernel32', $f, 'III', 'I' )
        or  die "Can't find $f() in kernel32.dll: $^E\n";
    my $l= 512;
    my $s= ' ' x $l;
    my $a= unpack "I", pack "P", $s;
    my $r= $m->Call( 0, $a, $l );
    die "$f failed: $^E\n"
        if  ! $r;
    $s= substr( $s, 0, $r );
    return $s;
}
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