to my knowledge the easiest version of this manoeuvre, if you still have feature-1, is

    git checkout feature-2
    git rebase feature-1 --onto master

rather confusing. is there a better way?

edit: oh, you mentioned extra commits on master since the squash of feature-1. does that require two rebases?

    git rebase feature-1 --onto master-at-feature-1
    git rebase master