It's all just diff and patch anyway, RCS doesn't particularly add anything to that. I have been assuming you've tried diff and patch already and not been happy with the result? If not, try that first.
Code:
mv file file.mine
sd revert file # or whatever the command to revert is
diff -u file file.mine >mine.patch
sd get # or whatever you do to bring in the latest version
patch <p0 mine.patch
# pore over conflicts
sd commit
rm file.mine mine.patch
It's been a long time since I used RCS, but if I remember correctly, even CVS brings substantial improvements to conflict handling in particular. There's nothing to prevent you from checking the files into a local CVS repo, save for the CVS directory which might upset another version control system, and/or need manual sync if you use another version control in tandem.
