It might be easier to upgrade your perl to 5.14:

$ perl-5.14.2 -wE 'say "\xA0" =~ /\s/'
1
$ perl-5.14.2 -wle 'print "\xA0" =~ /\s/u'
1
$ perl-5.12.2 -wE 'say "\xA0" =~ /\s/'

$
[download]

Alternatively, upgrade your string to UTF-8:

$ perl -wle '$_ = chr 0xA0; utf8::upgrade($_); print /\s/'
1
$
[download]