You might also like to consider Create Edition-specific Fat32 InstallUSB - [my post #555] - TenForumsTutorials because the steps described apply equally well to reducing the size before writing to a DVD.

I suspect that the easiest way to manage it in the case of a DVD would be to
- extract the ISO contents to an intermediate location on a hard drive,
- do the work of reducing the install.wim in the manner described in the link,
- copy that reduced .wim into that intermediate folder [overwriting the original .wim in the process],
- copy the intermediate folder to the DVD.

Denis