The tool I'm working for (ECMerge) as a preview function. It allows you to apply a patch (reverse) in a file, as well as visualize the other side or simply βtellβ if it is applied as a whole. When creating the other side, it can paste into the clipboard what was rejected. It has the usual options for restricting context and moving applications. Patch files have syntax coloring.
Once you can apply the patch the way you want, you have a two-way merge view, so you can choose what you finally want to apply, save, or create corrections.
It is not perfect, but it is workable.
armel source share