You can use a Z Depth or World Position Pass
to integrate other layers. What you could do is use a duplicate of your Element layer, set the duplicate to Z Depth from the Output/Show. You can then set that layer as a track matte for another layer to get it to appear behind an object.
Use a Z-pass render to combine 2D stock footage
• Use most 3D programs like 3D max, C4D & even Element 3D
Control the start depth (white) and how it transitions to the End (black).
Control the position of the Depth (black)
Limits the maximum depth value to 1 when using 32bpc.
Makes background transparent