I at one point did a couple of macros to achieve the goal more or less. I basically copied roomtone throughout on an adjacent track, say above for example (I can’t remember now). So that tone filled that track for the duration of the dialog to be edited. Then while editing I would just select the range on the dialog track where I wanted roomtone instead and hit the macro key. The macro would delete, move up one track (selection maintained), copy, move back down, paste. There was one problem with this and I can’t remember what it was. If I have time I’ll look for it here in the forum later.
The good thing about it was that I created an alternative and had a modifier key trigger it. So if the above was “F” then “Alt F” would cut instead of delete, move down one track and paste, move up two, copy, down, paste. The point of that was for those instances where you want to extract sounds for a dedicated PFX track.
Come to think of it, I think the problem was in creating x-fades.
Either way, in my opinion, this is what makes Nuendo a fantastic app.