What about using something like '%8.3g', just like with C ?   Or even '%8.3G' if you really want the uppercase 'E'.

perl -e "$f=1.567E-09;printf qq{  '%s'  is  '%8.3g'$/}, $f, $f;"
  '1.567e-009'  is  '1.57e-009'

perl -e "$f=1.567E-09;printf qq{  '%s'  is  '%8.3G'$/}, $f, $f;"
  '1.567e-009'  is  '1.57E-009'

If you need to force only two digits on the exponent you might have to resort to an RE?