Setup a layered texture node feeding whatever channel (diffuse) for example.
Layer your image files into the layered texture.
Select all of the image nodes and go to the attribute spread sheet. Turn all default color RBG values to 0
For each 2D placement node, turn off Wrap U and Wrap V
In the Attribute Editor for the Image Node:
Set UV Tiling Mode to Explicit Tiles
Change the U and V values to reflect each image's placement along the UV tiles.
The coordinate system is 0 based so if you had your head texture on the second UV tile (one right of the default) the values would be U=1 V=0