The git svn rebase trick described earlier does almost exactly what Alf wants.
You're absolutely right. With the rebase, I have my history (which so
far is linear) in the SVN repository, and I can continue using git
locally and pushing my commits back to Subversion. I also want to try
Björn's suggestions about merging SVN branches. While Subversion
fixed the most annoying problems in CVS, I think it got a lot of
branching, merging, and tagging wrong. Maybe using git to handle
merging will make a nice band-aid.
Anyway, thanks to all for the suggestions!
-Alf