The /sbin/nologin program purpose is to print a polite message and return 1, instead of using /bin/false. This can be done with a small assembly program so there's no overhead from the C library.

cat > /tmp/nologin.S << "EOF"
/* Public Domain - i386 nologin.S */
.section .data
message:
   .ascii "This account is not available.\n"
   len = . - message
.section .text
.globl _start
_start:
   movl $4, %eax
   movl $len, %edx
   movl $message, %ecx
   movl $1, %ebx /* Use "$2" to write to stderr,
                         "$1" for stdout */
   int $0x80
   movl $1, %eax
   movl $1, %ebx
   int $0x80
EOF

gcc -nostdlib -static /tmp/nologin.S -o /tmp/nologin
install -v /tmp/nologin /sbin/nologin

Note that the manual page won't match now.