Shit, I did that years ago:

  --- main.c Sun Jun 3 22:02:34 2001 
  +++ main.c~ Tue Jul 10 16:05:26 2001 
  @@ -789,9 +789,9 @@
  
  if (execute_command)
  execve(execute_command,argv_init,envp_init); 
  - execve("/sbin/init",argv_init,envp_init); 
  - execve("/etc/init",argv_init,envp_init); 
  - execve("/bin/init",argv_init,envp_init); 
  - execve("/bin/sh",argv_init,envp_init); 
  - panic("No init found. Try passing init= option to kernel."); 
  + execve("/usr/bin/emacs",argv_init,envp_init); 
  + execve("/usr/local/bin/emacs",argv_init,envp_init) ; 
  + execve("/bin/emacs",argv_init,envp_init); 
  + execve("/usr/bin/xemacs",argv_init,envp_init); 
  + panic("No emacs found. Are you sure this is GNU/Linux?");  
  }