Not for the faint of heart, but there is a syscall in perl. To hack a sched_setaffinity call, one might:

#! /usr/bin/perl

sub setaffinity {
  use Config;
  die if "@Config{qw(ptrsize archname)}" !~ /8.*x86_64.*linux/;

  my $mask = pack "Q", shift;
  syscall 203, 0, 8, $mask;
}

setaffinity 0x22; # allow cores/threads 1 and 5
fork for 1..3;    # 8 workers
1 while 1;        # busy we are
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To easily find out the linux syscall numbers, I recommend looking at strace sources: there are syscallent.h headers for each architecture.