Is there a way to configure vimdiff to ignore ALL whitespaces?

I'm using `vim -d file1 file2` in order to see the differences between them. This works fine, but I want to ignore whitespace changes - they are irrelevant for source code files. Vim help states that the following command will do the magic: ``` set diffopt+=iwhite ``` But unfortunately, this command only adds `-b` to diff tool command line, and that only ignores trailing whitespaces. The correct command line key for diff should be `-w`, to ignore all whitespace changes. But I can't find how to modify the diff command line directly from Vim. Of course I can compile a custom diff, or replace diff with diff.sh, but that looks kinda ugly :(. Is there a better way to modify how Vim interacts with the diff tool for displaying file differences?