This article gives some good ideas about how PhD students can support each other in the writing process, and also help create a sense of community. Would anybody be interested in a potential Space Group writing session now and again?
By writing regularly, and for shorter periods (2-3 hours a day), you remove some of the fear related to writing, and binge writing in particular. Writing, like any skill, is something that you need to practice to improve at; by being in a writing group you ensure (at least) two hours per week of protected writing time. Furthermore, writing in a group is incredibly motivating, so as long as you turn up you will likely be focused during the session. Often my most productive part of the week is in my writing group(s).