Or, keeping in the spirit of this lightweight approach, i.e. not bringing a hash to bear on the problem, if you want to munch @_ with shift you will have to do something like:

#! /usr/bin/perl -w

use strict;

sub x {
    # my $one = do { @_ ? shift : 'default' };
    # my $two = do { @_ ? shift : 43 };
    my $one = do { my $arg = shift; defined($arg) ? $arg : 'default' }
+;
    my $two = do { my $arg = shift; defined($arg) ? $arg : 43 };

    print "x($one, $two)\n";
}

x();
x( 'this' );
x( 1, 2 );
[download]

update: sheesh, misread a requirements document and get downvoted into oblivion. I corrected the code; you can stop now. The principal idea I wanted to show was that a do block is a pretty nice way of doing this, because the default value appears at the end of the code, making it easy to spot, thus letting you gloss over the mechanics.

print@_{sort keys %_},$/if%_=split//,'= & *a?b:e\f/h^h!j+n,o@o;r$s-t%t#u'