There is a fuse-fs for browsing rdiff-backup repositories [1].
Passing options to fuse is going to be enabled in the next release. With
allow_user set I should be able to mount my config backup as root, but
browse it as a user.
There's also a nice way to automatically exclude filesystems that do not
correspond to block devices listed in /dev. E.g. proc, tmpfs, but also
fuse.
Haven't tried it yet, but this should work:
rdiff-backup --exclude-filelist<(grep -v '\(^/dev/\|^rootfs\)' /proc/mounts
| cut -d \ -f 2 | uniq) \
<other options>
Best, Andreas
[1] http://code.google.com/p/rdiff-backup-fs/