This question is why I found this site, because I was looking all over for the feature and could not find it. I know what you mean because you see what you want RIGHT before you release the mouse button. Then they take it all away when you release! Such a simple option, I can't understand how they wouldn't have it.
Eventually I came up with a workaround.
For some reason the suggested workaround here and on Adobe forums is to make your selection to clip your modifications...then a really gigantic clone stamp brush size (bigger than the size of your area). Then go around clicking control on your source and then try and position that source in the destination.
That is backwards of what you wanted. You wanted to mark the area you were replacing first, then drag around over choices of source until the replacement area looked right. Clone stamp can't do that, so I don't know why people think that's a solution.
You can do it with some labor using layer masks. You just have to un-link them from the pixels:
duplicate the layer you want to copy from
mark out a selection on that layer the way you would if you were defining the target area for the patch tool, just use ordinary selection tools
when you have your selection set, add a layer mask on this duplicate layer so it masks only the selection
click the chain link which is between the mask and the image that makes them move together. the chain link disappears which means you can move each of them independently
select the image on left (not mask, on right) and move that around. The mask will stay in place and it's like you're sliding the source image around in a "window" the mask defines
you are done but the final step is to write a letter to Adobe and ask this to just be an option in the patch tool
It's the kind of thing that you think "what a hassle" at first but it's a quick few steps, if I knew anything about scripting it I bet you could make it more automatic.