Access to root files when SSH root access is disabled

I have disabled root access to SSH, which has also disabled direct access to root FTP.

There is one user who is on the wheel group and can access root via SSH, using su and modify/delete/create files.

Via SFTP, however (using SSH Keys via Pageant), this happens: the same user has access to all the files, without entering any su credential, but of course cannot modify them.

So, I was wondering:
Is there a way for WinSCP to temporarily give that user the ability to edit root files? Much the same way we do with su via SSH?

See How do I change user after login (e.g. su root)?