You want to retain bootability with the 200MB image and still use the remaining space on the DVD.
If your DVD Writing software lets you create multiple sessions with the first one carrying the bootable 200mb image and the later session carrying data, this could possibly work.
It would also require the ability of letting the first session remain bootable.
Have never actually tried it.
Why not use a CD instead of a DVD and forget the lesser wasted space?
Or, even the 3+ GB on a DVD -- these media are quite cheap.
You might end up wasting more media in these attempts.
Maybe, you have a mass production interest in which case getting this working (if feasible) might be worth a few attempts.