Blender's script to create Envelope display type Armature like mesh.

Armature2Mesh.py

import bpy
import math
import mathutils
from mathutils import Vector
from mathutils import Matrix

for selobj in  bpy.context.selected_objects:
    #print("{} is {}".format(selobj.name, selobj.type))
    if selobj.type == 'ARMATURE':
        arm = selobj.data
        # print("Armature {} contains {} bones".format(arm.name, len(arm.bones)))
        if len(arm.bones) <= 0:
            print("Armature {} has no bones. skip it.".format(arm.name))
            continue
        
        verts = []
        faces = []
        vgroups = []
        for abone in arm.bones:
            """
            print("{} length:{}".format(abone.name, abone.length))
            # from parent bone
            #print(" head(loc:{}, r:{}".format(abone.head, abone.head_radius))
            #print(" tain(loc:{}, r:{}".format(abone.tail, abone.tail_radius))
            #print(" matrix:\n{}".format(abone.matrix))
            # from armature
            print(" head(loc:{}, r:{}".format(abone.head_local, abone.head_radius))
            print(" tain(loc:{}, r:{}".format(abone.tail_local, abone.tail_radius))
            print(" matrix_local:\n{}".format(abone.matrix_local))
            """
            head_r = abone.head_radius
            tail_r = abone.tail_radius
            bone_len = abone.length
            tmpverts = [
                Vector((-head_r, -head_r, head_r)),
                Vector(( head_r, -head_r, head_r)),
                Vector(( head_r, -head_r,-head_r)),
                Vector((-head_r, -head_r,-head_r)),
                
                Vector((-head_r, head_r, head_r)),
                Vector(( head_r, head_r, head_r)),
                Vector(( head_r, head_r,-head_r)),
                Vector((-head_r, head_r,-head_r)),
                
                Vector((-tail_r, bone_len-tail_r, tail_r)),
                Vector(( tail_r, bone_len-tail_r, tail_r)),
                Vector(( tail_r, bone_len-tail_r,-tail_r)),
                Vector((-tail_r, bone_len-tail_r,-tail_r)),
                
                Vector((-tail_r, bone_len+tail_r, tail_r)),
                Vector(( tail_r, bone_len+tail_r, tail_r)),
                Vector(( tail_r, bone_len+tail_r,-tail_r)),
                Vector((-tail_r, bone_len+tail_r,-tail_r))
            ]
            tmpfaces = [
                (3, 2, 1, 0),
                
                (0, 1, 5, 4),
                (1, 2, 6, 5),
                (2, 3, 7, 6),
                (3, 0, 4, 7),
                
                (4, 5,  9,  8),
                (5, 6, 10,  9),
                (6, 7, 11, 10),
                (7, 4,  8, 11),
                
                ( 8,  9, 13, 12),
                ( 9, 10, 14, 13),
                (10, 11, 15, 14),
                (11,  8, 12, 15),
                
                (12, 13, 14, 15)
            ]
            voffset = len(verts)
            tmpvgrp = {'name':abone.name, 'verts':[]}
            for i, v in enumerate(tmpverts):
                verts.append(abone.matrix_local * v)
                tmpvgrp['verts'].append(i + voffset)
            vgroups.append(tmpvgrp)
            for f in tmpfaces:
                faces.append((f[0]+voffset, f[1]+voffset, f[2]+voffset, f[3]+voffset))
        
        #print(verts)
        #print(faces)
        #print(vgroups)
        
        # create meshes
        newname = arm.name + "_mesh"
        newmesh = bpy.data.meshes.new(newname)
        newobj = bpy.data.objects.new(newname, newmesh)
        newobj.matrix_world = selobj.matrix_world
        bpy.context.scene.objects.link(newobj)
        
        newmesh.from_pydata(verts, [], faces)
        newmesh.update(calc_edges=True)
        
        for vg in vgroups:
            newvg = newobj.vertex_groups.new(vg['name'])
            for vid in vg['verts']:
                newvg.add([vid], 1.0, 'REPLACE')
        
        submod = newobj.modifiers.new('Subsurf', 'SUBSURF')
        
        armmod = newobj.modifiers.new(arm.name, 'ARMATURE')
        armmod.object = selobj
        armmod.use_bone_envelopes = False
        armmod.use_vertex_groups = True
        
        arm.draw_type = 'OCTAHEDRAL'
        selobj.show_x_ray = True