You can use Symbol::gensym on such old perls to get lexical filehandles (more awkward, but gets you the same benefits), and you could write a conditionally installed wrapper to emulate three-arg open (only awkward once, but only worthwhile when you can foresee value in making the code easily forward-upgradable). Whether the effort is justified will depend on your particular circumstances, of course (but see also my signature).

Makeshifts last the longest.