So, thinking about it for a bit, we could actually try to create a chimaera today if we have an hour or two free in our schedule. It'll be a bit more difficult without Niko's matter reconstruction, but we may be able to substitute for that.
What we need:
-One (1) Witch
-One (1) human body (fresh and unoccupied)
-An incredibly deep knowledge of human physiology and anatomy (optional)
-The ability to be conceptually completely fucking broken
-One (1) stasis bottle (optional)
-A memory altering device (optional)
This is all based on educated guesses as to what chimaeras are and how they work; even if we don't get around to it in the next couple days, it's at least a hypothetical starting point since (Michiru still being alive) Niko probably hasn't even started on this line of research.
What do: First (after hatching it if necessary), we tear the Witch into bloody chunks until it dies, but hold onto those chunks with our sadkinesis so that the Grief Seed doesn't reabsorb them; if we can't keep them frozen under our conscious control without altering them, we stuff them into the stasis bottle (which should be a trifle to griefhack, since we know what it is and approximately how it works).
Since we won't have a human body handy, we'll need to make one: We could probably griefhack a machine that reconstructs matter on the molecular level, but this may or may not be permanent outside of our control radius, which could get messy; if it doesn't work, we can use it as a prototype to enchant a genuine article off of (with Mami's help, likely; she doesn't need to know what it'll be used for right now).
Next, we need to implant the human body with the witch fragments, and connect the Grief Seed to it: The Grief Seed is still the (remains of the) Magi's soul (gem), so it will act as the motive force for the body. Witches don't use magic per say: It will instinctively attempt to control/absorb its body (the fragments) with its innate grief control, and will take control of the body in so doing. In theory, it will also instinctively slave its cognitive functions to the familiar hardware of the body's physical brain in the same manner that the vast majority of magical girls do (having lost its original body on apotheosis), filtering the original personality from the Seed to the body and away from the mass of Grief, thereby allowing the witch to function as a sane and autonomous being without hatching. This is where memory auditing comes in: If the chimaera retains all of its memories, she will remember the trauma of dying and becoming a Witch: Depending on the closeness to which she identifies with the former magical girl and general mental state, this can cause a relapse; anything from going berserk/feral to hatching the Grief Seed.
In fact, our particular powers may give us an edge here: Grief is the fuel Witches use to produce phenomenal effects (in the chimaera's case, pseudomagical effects and Magi-esque transformation), but is also the physical manifestation of psychological damage; mostly or completely emptying out a Seed before connection may result in a more stable chimaera, if possibly a less combat-capable one.
