Please forgive a non-flyer poking his nose in.
There is an interesting video on youtube of a 737-900 I believe, performing a takeoff with an un-secured Captain's window, which opened shortly before the rotation occured. It was filmed (I believe) by Boeing to demonstrate that a safe takeoff could be accomplished with an open window, rather than a pilot performing an RTO with all it's inherent effects.
Coming back to your point, the video shows the Captain using clear visual signals to ask for gear up and also transferring control to the FO so he can use both hands to secure the window.
I would post the link for you but alas, Mcafee will not permit it...