Here's a different approach. I may benchmark this later:

$newword = join '', split(/(\w+)\1/, $word);
[download]

Whoops, missed the + the first time! Let's say the first was a warm up, and the second actually works:

$newword = join '', split(/((\w)+)\1(\2{0,1})/, $word);
[download]

There. Appropriately hard to read.

Update: Yes, I had the backreferences backward, which breaks things, as the Anonymous Monk points out below. That'll teach me to be crafty.