De acordo com o blog deles, agora é possível fazer isso no instantâneo 1.10.
Aqui está a parte relevante da postagem do blog (ênfase minha):
We have had a long standing request for the ability to dock Developer Tools. Well, wait no longer, we are introducing this handy feature in our very first 1.10 snapshot. All of you developers who desperately wanted this, can now breathe a sigh of relief. Of course, if you prefer them undocked, that still works too!
Editar: eu baixei 1.10.838.7 e posso confirmar que funciona.