Can you post some screen caps or examples of exactly what you're trying to accomplish? Some of the descriptions so far seem conflicting and I'm not sure I follow you.
Just for clarity:
You mentioned Angela Anaconda at the head. I finally got around to looking at some the old videos on YouTube. Oh, yeah, I remember that!
If you step through the footage, you'll see that it's all done with still photo elements, no 'warping' involved. You can replicate that using basic switch layers and a series of photos. You mentioned wanting a 'lazy' way to do this, and the 'layziest' is probably to shoot all the faces and mouth shapes, chop them up in Photoshop, and then place the elements in separate switch layers. At minimum, you'll want a single Face switch with all the possibilities, but what would look better is an Eyes switch and a Mouth switches over separate static 'head' layer would look better, and it would be exactly like Angela.
If you want to add some nice subtlties, use a mesh and link all the elements to the single mesh, and use the Magnet tool or pin bones to warp it. But that's already going way beyond what you see in the Angela footage.
If your photo source is limited, you can paint variations of the head features in Photoshop. Liquify in Photoshop is awesome for this, especially now that they've added tools
specifically for altering the human face. I've done this sort of thing with painted human faces at work, and it saved me from painting too many variations from scratch. Again, it's a little more work, but if you're not going to shoot enough actual photos in advance, it's a good alternative approach.
If you want to do it 'right', you'll want to break the face down into more elements: separate switch groups for each eye and the mouth, and and breakout the eyebrows with their own bones or mesh. You might even make separate the nose for 'wrinkling', etc. Of course, now were getting a lot less 'lazy' about the possibilities...but it's still not terribly complicated stuff.
And there are other cheap tricks you can use to make it look much smoother than Angela. For example, if you break out the mouths to their own Switch Layer, you can put a lot of life into the lipsync by squashing and stretching the group layer. Just set the origin to the upper lips, and then you can credibly transform the group as a whole. I recommend doing the S&S as a second pass,
after you've completed the lips sync pass--it will get too complicated and messy to do both at the same time. Oh, and don't forget to add a pin bone to the chin so you can drop the jaw appropriately. Both, the Lipsync switch and the jaw-mover can be linked to Smart Bone dials to make it easier to animate, and if you set it up right, you'll still have flexibility to add your own manual tweaks on top of it. But, yeah, we've gotten pretty far away from 'lazy' at this stage.
Just wondering, which version of Moho are you using? Pro or Debut? Only Pro allows you to create and edit a custom mesh. A single mesh layer can be shared by any number of vector or image layers, so that shouldn't be a limitation. However, where you place the mesh layer may prevent some layers from accessing it, so make sure you're using the mesh correctly.
Much of what I think you're describing can be accomplished a number of ways: Using Switch Layers with static images, using animated meshes and/or bones to deform static images, animated layer order, animated shape order (texture filled shapes all in the same layer,) masking tricks, or a combination of any of these techniques. All the tools are there, it's a matter of knowing what you want to do with them.
Earlier, I mentioned Liquify in Photoshop. If you have After Effects, Liquify also exists there and it's fully keyframeable. I sometimes use this to add subtle (and sometimes not so subtle) deformations to my Moho renders. It's very useful for getting a little more expressiveness out of limited image resources.
Because there is a wide range of tools and possibilites, I suggest designing a character with
specific techniques in mind, and then creating a simplified version of the concepts you wish to test. Once you've proven your method, apply what you've discovered or learned to your finished character. This is pretty much my workflow for every new character and design, whether it's for my own stuff or a production I'm assigned to work.