The same like in 3dsmax. Attach polygons via Maya Python Api and Maya cmds to existing mesh.
Not combine, no cheating. Also with skinning support.
Limitation : very slow.
Download : attachObjects.zip
Just unzip the script into C:/maya_scripts/modeling and make a Python shelf button in Maya with this code:
import sys import maya.cmds as cmds path = 'C:/maya_scripts/modeling' if path not in sys.path: sys.path.append(path) import attachObjects; attachObjects.main();