Add bones instead of average when a vertex is in two groups

Is there a way to make Blender consider vertex group weights by adding instead of averaging when posing an armature? The way Blender 2.7x has worked for me so far is that when a vertex belongs to a vertex group (with a weight of 1) of two bones it splits the weight 50/50 between the two bones. If I move one bone by (1,0,0) and the other by (0,0,1), the vertex would move by (0.5,0,0.5). What I’d wonder if there is a way to get the vertex to move by (1,0,1) instead. This way would also mean if the two bones were both moved by (1,0,0) then the vertex would move by (2,0,0).

I experimented with making a bone a parent of another with shared vertices and that did not affect the way the vertices moved. If vertices were added instead of averaged then I anticipate possible complications with parent/child bones sharing vertices. If I moved both the parent and child by (1,0,0) then adding could result in it moving by either (2,0,0) or (3,0,0) (since the child bone is moved by 1 by the user and another 1 inherited by its parent).

The reason I ask about this is I’ve been using bones (with drivers) to modify deformations in an armature. Like the way if a straw is bent it pinches; an arm doesn’t pinch but rotating bones in Blender behaves more like the straw. I have used shape keys for this in the past but I have a lot of problems with shape keys, party because it takes a large amount of memory, a mesh with shape keys can’t be edited, and problems with Python scripting. I read that Blender can be set to animate everything, including individual vertices, but I also read that with this option Blender keeps animation data for all vertices, including those that are not moved, which consumes a lot of memory.

I’m not sure but I think I recall Blender 2.4x adding bones transformations instead of averaging.