You can use the code assertion regex to do this. (See perlre "Extended patterns" for details).

P:\test>perl -Mstrict -wle"
    my $s = 'the quick brown fox jumps over the lazy dog';
   my @bits; 
   $s =~ s[
        .(.)(?{ push@bits,$^N })
        ..(..)(?{ push@bits,$^N })
        .]
   [ print join'-',@bits; ]gex;"

h-qu
h-qu-k-ro
h-qu-k-ro- -x
h-qu-k-ro- -x -m- o
h-qu-k-ro- -x -m- o-r-he
h-qu-k-ro- -x -m- o-r-he-a- d
[download]

Note: I've split the 'one-liner' up to avoid the code wrap mangler.