Defining geometry with two 3D meshes adjacent to each other

I am considering the heat flow problem in PDE toolbox. I want to define two objects: a table surface and an object on the table. The meshes for the table surface and the object can easily be defined by the meshgrid command. In order to define it as the geometry of my PDE model, I use convhull function to obtain the nodes and elements for each individual object. Since element numbering starts from 1 for both objects, I add a constant number (which is the total number of elements in object1) to the elements of object2 and create the geometry. However, since the points at the intersection region of the objects are defined by two different node numbers (one for object1 and one for object2), the face at the intersection has two face numbers and PDE toolbox recognize the model as two individual objects.

I know it is possible to check the intersection points in a loop and avoid double-node-numbering but as the number of objects increases in my system, it will take long time. Is there any easy method to automatically generate a geometry from multiple meshes?