I believe it is already done: Getopt::Mixed. The syntax is slightly different from Getopt::Long, so it isn't a drop-in replacement. Also, by default, it exports a bunch of scalars into the calling package (bad, IMO) -- the non-default behavior is pretty nice, though:

use Getopt::Mixed 'nextOption';
Getopt::Mixed::init('option1=s>o', 'option2:i>o2');

my %opt = (
   option1 => 'default1',
   option2 => 'default2',
);

while ( my ($k, $v) = nextOption() ) { $opt{$k} = $v }

Getopt::Mixed::cleanup();
## what's left is now in @ARGV
[download]

Using nextOption lets you process serially, too, which can be nice sometimes.