Well the solution was pretty simple, hinted by Pat Notz and Bombe.
#Make sure we're on the master branch
$ git checkout master
# Make a new branch to hold the work I've done
$ git branch old_master
# Save this branch on my remote repo (for backup)
$ git checkout old_master
$ git push origin old_master
# Reset my local master back to match the commit just before I started
# working on my new feature
$ git checkout master
$ git reset --hard 2aa93842342342
# Get it to be the same as my Central
$ git pull upstream master
# Now DELETE my master on my remote repo
$ git push origin :master
# And recreate it
$ git push origin master
# Branch created!
#* [new branch] master -> master
#
Now I have two nice branches: master and old_master. With master being a copy of my Central, for fixes to production, and old_master holding all the work that I did previously!
Thanks!