Rebase feature branch onto older revision of master

Let's say, I have a feature branch b1 based on branch master. After rebasing it to the newest version of master, I realize there's a problem and want to go back. But I cannot rebase b1 onto an older revision of master because the path from the new base commit to my feature branch head includes the commits of master.

Currently, I create a new branch at the new base commit and cherry-pick all the commits of my feature branch. That works but requires to create a new branch with a new name.

I'd propose to add a rebase option that allows to choose the branch to be rebased (maybe only visible if there's the need for it). Rebasing then starts with the first commit of that branch. If there is a sequence of branches (b1 based on master, b2 based on b1, and so on), smartGit could offer a list to chose from.