Isn't this exactly the modus operandi of the Mind Flayers?
If not just food, you have a larva put into you that transforms your physical form to an illithid and are not part of the hive mind.
Or, a third option, you are twisted into a new form of thrall that meets the colonies needs.
Another option is vampires. While it is not their typical flavor, you could take the idea that vampires are connected to and controlled by their creator and ramp it up to 11. A vampiric borg race spreading like the plague. Oh, right, you said no undead. Him, reskin a vampire into a non-undead or make a lycanthrop have a similar link to its creator?
Myconids are another classic monster that is not undead, has a kind of hive-mind via spores and can transform other creatures into fungal creatures. When the sovereign takes damage all myconids nearby feel the pain. While the reanimating spores create a fungal drone from a corpse ( I would rule it to be a fungal creature and not an undead one), you could homebrew that so that living creatures could be turned into spore servants, not just corpses.
Another option that would be pretty awesome would be a cult of Wizards who use enchantments, evocations, and transmutations to effectuate a borg-like society, bring in new members willingly or unwillingly based on characteristics they desire from the group and which they can study and work into a program to create an ever-evolving master race. Just a few tweaks would be needed. Perhaps they have experimented on dopplegangers and applied what they learned to themselves.
Some spells from core books that would add to the flavor of the group:
* Alter Self - they will use alter self to take on desired traits. At low levels it is temporary, but at higher levels, perhaps they are able to make the alterations "stick" and become a permanent part of their normal form.
* Create Homunculus - it makes sense that such a cult would create beings from their own blood that have a telepathic bond to them and go out to spy, conduct reconnaisance, run errands, etc.
* Dominate Person - useful to get control over desirable "recruits"
* Enhance Ability - but instead of hair/fur from a beast, perhaps they can use hair, nail clippings, blood etc. from a human to enhance their abilities temporariliy. So they will want to take in new members that have attributes they tend to lack in.
* Feeble Mind - weak the minds of those they want to abosorb into their group.
* Modify Memory
* Polymorph - they would have an interest in magics that allow them to take the form of other creatures or to put others into the forms of other creatures are part of their experiments.
* Shape Change -- I would alter a bit to either allow, say 6 or more low-level members to cast this as a ritual and if they continue the ritual for 24 hours, the creature is takes on the shap of the new creature permanently unless greater restoration is cast. This is how they try to continue to better them selves and transform those brought in.
* Skill Empowerment - toch a creature to give it expertise in a skill of your choice seems to fit the flavor of a borg-like magic cult.
* Telepathy - I might make this a group feature. Perhaps they have some artifact in their home base or they have just developed the ability and newly transformed members inherit it.
Hmmm...I'm starting to like my doppleganger wizard borg cult. I might have to find a way to use that.
