We've just updated the site so you can now "End Review of Version" from the "Manage" page of the proposal. I went ahead and did this for you. Thinklab is not the really intended as a tool for collaborative writing, so it makes sense that you're doing that in Google Docs. Thinklab would come back into play if you had a more complete version that you wanted to have reviewed. (There's an "Open for Review") button. I guess there's not a lot of time left now :)
As you can see, this is a bit of a challenge. Typically we end up writing in Google docs until the last possible moment. To use ThinkLab effectively would require a lot of discipline in terms of self-imposed deadlines that were sufficiently in advance of actual hard deadlines to allow for the process to unfold. No one would argue that such discipline would improve the end-product, ThinkLab or not. I can tell you from my personal situation over the past 2 months leading up to this particular proposal that the delay was not for lack of trying.. Just too many things to do that are all top priority.
I think its worth thinking hard about the relationship between ThinkLab and real collaborative editing. If you could embed a live Google doc as an entity in this framework, you might make more progress in opening up the entire process. I'm not sure if the citable, frozen versions are the best things during the creative process. In cases like this proposal and Toby's earlier one, I think it would be better if things could be adapted quickly in response to feedback.
Now if you could make it such that the agencies that hand out the money made ThinkLab a necessary stop on the way to submission, you would get the missing 'real' deadline that would be needed to make this really work.