Figured it out...
%%File : sfun_Single2FourBytes.tlc
%%Description:
Real-Time Workshop interface for S-function "sfun_Single2FourBytes.c"
%implements sfun_Single2FourBytes "C"
%function Outputs(block, system) Output
/* S-Function "sfun_Single2FourBytes" Block: %<Name> */
%assign in = LibBlockInputSignal(0, "", "", 0)
{
union {real32_T x; uint8_T c[4];} sp;
sp.x = %<in>;
%foreach i = 4
%assign out = LibBlockOutputSignal(i, "", "", 0)
%<out> = sp.c[%<i>];
%endforeach
}
%endfunction
%%[EOF] sfun_Single2FourBytes.tlc