It sounds a little like nage is sitting still when the attack comes.
Get to knee walking! Maybe the dojo where I train is different than most, but we're allowed to "break the ice" with other techniques so long as we finish with the technique that sensei asked for. The element of surprise is a very valuable tool. If your uke is taking for granted that you're going to hold still and let him grab or hit you, wake him up!
Move your hand just a little. Get him to advance just a little further than he planned. Take his balance and have fun!