I managed to use KEY_WOW64_32KEY and KEY_WOW64_64KEY without modifying Win32::TieRegistry:

use Win32::TieRegistry qw(:KEY_);

sub KEY_WOW64_64KEY {return 0x100;}
sub KEY_WOW64_32KEY {return 0x200;}

my $Reg32={};
my $Reg64={};
new Win32::TieRegistry("HKEY_LOCAL_MACHINE", {
    Delimiter=>'/',
    Access=> KEY_READ|KEY_WRITE|KEY_CREATE_SUB_KEY|KEY_WOW64_32KEY } )
    ->Tie($Reg32);
new Win32::TieRegistry("HKEY_LOCAL_MACHINE", {
    Delimiter=>'/',
    Access=> KEY_READ|KEY_WRITE|KEY_CREATE_SUB_KEY|KEY_WOW64_64KEY } )
    ->Tie($Reg64);
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