Fossil SCM

I'm missing a feature to add only parts of a file, not a whole file at once. This is important for me to keep commits focused around a specific topic.

Current workflow in fossil:

edit some-file.rb
# hacking away, i have an epiphany that solves most of the
# problems on earth, so i implement it before i forget it again.

cp some-file.rb some-file.rb.bak
# I noticed that I actually solved two different problems, so
# I would like to announce them separately, but how?
# Right, by making a backup first...

edit some-file.rb
# Now I removed one of the features, leaving only one in the file.

fossil add some-file.rb
fossil commit -m "Add the feed_the_world method"
# well, you know what that is.

mv some-file.txt.bak some-file.rb
# and finally I move the backup back in place so the second
# feature can be added.

fossil add some-file.rb
fossil commit -m "Add the cure_aids method"
# and again commit that.

What I'd like to do instead, in case you are not familiar with git, is along the lines of the article here: [http://tomayko.com/writings/the-thing-about-git]. I didn't write it, but it pretty much expresses what I feel is missing in order for me to consider daily use of fossil. The description above is only about one file, now imagine having to do that over 5 files (average number of files in my commits).

Thank you, I'm really impressed otherwise. Maybe there is a feature that I haven't found in the documentation yet that helps with this?