How about creating a 1 to 3 sec color matte (video 2) which will center align between the clips (video 1). Then keyframe the Opacity of the color matte, 0% at the beginning of the color matte, 100% at the 50% point, and 0% at the end of the color matte.
I am not sure whether you would also want a genuine 1 to 3 sec Dip to White between the clips (video 1) at the same time. I road tested that and it seems to work for me.
Please let us know if that worked for you.
I will see what else I can find on the topic.