global alpha mapping across existing textures?

Hi, I was wondering if it is possible to map a texture over 2 objects that already have other texture. Example I have a character with 2 seperate pieces of clothing. Both pieces of clothing have uv mapped textures. I would like to map a blood spatter onto the 2 pieces of clothing.
Can I somehow map a png image (transparent background) of a plood splatter globally, so that only the blood spatter can be seen on top of the other textures? If so, I would love to know how.

thanks,

phlopper

http://wiki.blender.org/index.php/Manual/Texture_Channels