How to prefix existing svn remotes?

Hi all,

I created a few months ago a git-svn repository using: git svn clone -s https://my_svn_repo .

wich also created the following remotes:
git branch -r
  branch0
  tags/tag0
  trunk

I would like to prefix theses remotes, so that it shows:
git branch -r
  prefix/branch0
  prefix/tags/tag0
  prefix/trunk

Of course I should have used the -prefix back when creating the repo but it's too late. 'git help svn' doesn't explain how to achieve that and simply editing .git/config to add the missing prefix will cause the next 'git svn fetch' to download again the whole history (which in my case is huge).

Is it possible? Did I miss something obvious?

Cheers,