... you could overload syswrite to unpack the data into bytes before invoking the real syswrite...
Which is just what encoding layers exist for: 
% perl -C0 -we 'syswrite(STDOUT, chr(0x500), 1)' | wc -c
Wide character in syswrite at -e line 1.
       0
Exit 255

% perl -CS -we 'syswrite(STDOUT, chr(0xE9), 1)' | wc -c
       2
% perl -CS -we 'syswrite(STDOUT, chr(0x1000), 1)' | wc -c
       3
% perl -CS -we 'syswrite(STDOUT, chr(0x01_0000), 1)' | wc -c
       4

% perl -CS -we 'syswrite(STDOUT, chr(0x0100_0000), 1)' | wc -c
       5
% perl -CS -we 'syswrite(STDOUT, chr(0x1000_0000), 1)' | wc -c
       6
% perl -CS -we 'syswrite(STDOUT, chr(0xF000_0000), 1)' | wc -c
       7

% perl -CS -M-warnings=portable -we 'syswrite(STDOUT, chr(0x10_0000_00
+00), 1)' | wc -c
      13

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In reply to Re^2: Simplest Possible Way To Disable Unicode by tchrist
in thread Simplest Possible Way To Disable Unicode by JapanIsShinto

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