In theory that ought to be a relatively simple thing to do...
If you are starting from scratch with at CC repository, make a snapshot view, and use that as the SVN Checkout location.
Now edit your files, as required, and keep the versioning in one of the repositories - and the update the other one when applicable. But you should be working on your separate branch or equivalent, in order to isolate your changes, and only integrate with teams in the same repository, when you are absolutely sure that that both repositories can present a proper configuration, i.e. all changes are labelled in ClearCase or Tagged in Subversion.
What works nice for a couple of folders, provided you know what you do, and how it effects each repository. However if you have more than a few files and folders, and you can foresee the need for restructuring the directory structure, you should consider some tools support, because both Version control systems are versioning directories and the process of renaming or moving a file in source control is different.
If you insist on doing it manually, you should develop and follow an appropiate policy for maintaining the integration between the repositories.