How can I remove some commits in Mercurial that were applied to the wrong branch and then replay them on the correct one?

My colleague has committed twice on his repository on the wrong branch.

What is the most effective way to take those two commits, get rid of them and then commit them correctly under the right branch? (the changes have not been pushed)

We'd ideally like a way to do this from within TortoiseHG but of course, we'll use the command-line if it is the best option.