Noiz2
Sound Ninja
... Without it......you are going to need something there to make it sound natural.
You mean like a sound post? ;~)
If your doing ADR or even using a lot of wild lines you really do need to do some sound post. Part of the reason Hollywood can get away with things like ADR is that they are doing a full sound post. 90% of the time nobody, not even experienced editors, will be able to pick out what has been ADR'd in a recent (as in last 20 years or so) film. If you do it's almost always performance. There are far more "alt lines" used than ADR, and that is essentially like the wild lines your talking about, and people will catch probably less than 0.1% because the performance is a match.
The point is for the OP the closer you are to just bare tracks the harder it is to slip anything in and not have it stick out. Once you start to add things in post the more it's a benefit to really do a full sound post. In the above with a full sound post your backgrounds will stay consistent because you created them in post. The room tone is just for filling in little holes in the dialog where you cut something out. If you have enough background going on you will never hear the switch to ADR and back "sonically" but performance is a different beast.