It is possible with non-encrypted filesystem. E.g if your partition starts at the sector
34607104 and the sector size is
512, you go with:
mount -o offset=$((512*34607104)) /dev/sdX /mnt/foo/
The partition table entry may not exist, it doesn't matter.
mount will examine the filesystem and do its job (you can help with
I don't know much about dm-crypt plain but it appears you should decrypt the device (partition) first, then mount. Michael Kjörling's comment is useful:
losetup and particularly its
--sizelimit switches. Once you have a loopback device configured, you should be able to mount it normally.
I would change the last words to "decrypt it normally" to fit your needs.
There is also
dmsetup tool. It allows you to create a mapped device from chunks of various files/devices. E.g. you can hide your encrypted "partition" in several gaps between normal partitions inside one or more HDDs. Read my answer to another question and study
man dmsetup. Make your
/dev/mapper/barbaz franken-partition and have fun with plain encryption on it.
Hint: in the said answer I use
losetup to create devices from files because
dmsetup doesn't work with regular files. You will work with already existing devices. Use their
/dev/something paths when building the map for
dmsetup – no need for
losetup in this case.