Shape key deformation similar to bone animation

I have a nice animation of a gum squeeze bulb which is rigged to a bone and gets deformed by posing this quite nicely.
Please have a look at the two screenshots, first straigt up, bone is not rotated, and second is with bone rotated by 50°.
This is achieved through weight painting on vertex groups regarding the turned bone.

Now, since I am about to export this to blend4web and thus am not able to use armatures, I want to do this using shape keys. the exported scene has more constraints and is not that flexible compared to the blender scene. Shape keys are working for this, I already tried this out.
Now, how can I have such a smooth deformation using shape keys. I don’t have the option to do use differnet weights on the vertices, do I?

I am thankful for your thoughts.
Thanks!

Attachments



Looks like using Absolute shape keys might do the job here.

See the example with the dafodill animation…
http://wiki.blender.org/index.php/Doc:2.4/Manual/Animation/Techs/Shape/Shape_Keys/Examples

I don’t think so. Actually I only need the ability to use a mesh deformation that results from a bone movement as a shape key deformation. I can do that with relative shape keys I guess.