After some discussion, the solution needs the following steps:
1-Git hook: writes the sha1, git-describe or other info describing the snapshot of source being built to a file (Version.txt) in the local directory - this hook is run on every pull, fetch, etc
2-Version.txt: a file in the local directory that is:
a) a Build Action of "Embedded resource"*,
b) is added to git-ignore
c) contains the version info from git described in #1
3-Build event: will copy the text from the file into the appropriate assembly attributes:
a) for version into the AssemblyVersionAttribute,
b) for other info (git describe or sha1 into the AssemblyInformationalAttribute. I think we could do this via variable substitution.
*May not have to be an embedded resource, maybe just a file on disk.