As Gregiboy said, it is impossible with any remux or passthrough profiles. You can modify any of the re-encode profiles for the output size that you want. Usually there is a line like this:
Change it so that it reads like this and try it.
If you want to lock this output size, change "limited" from 0 to 1.
Note that this modified profile will be overwritten when you update DVDFab, so store a copy somewhere else and copy it to the Profiles3 folder after the installation. It may be possible to do all this with the new Profile Editor, I have not used it yet.
