Lump commit HOWTO?

Hi All,

I have a specific workflow in mind that I'm not entirely sure how to
accomplish with git.  What I'd like to do is track a project in a
local branch, and do commits of my own there as well.  Then when I'm
ready to submit the work, I want to take all the incremental commits
and lump them into a single new commit and push that out as a patch or
into a branch for people to pull from.

E.g.

1) clone upstream into foo branch
2) commit A
3) commit B
4) pull upstream changes into foo branch
5) commit C
6) commit D
7) repeat steps 2 - 6 in various orders
8) take all local commits (A - D) and create a single commit without
any of the upstream changes in it

Is something like that easily accomplished?  Or perhaps a different
workflow that would allow similar results?

josh