Not quite sure if this will solve your problem or not but I helped someone awhile back get a decal w/transparent bkgnd onto a coffee mug and posted a step-by-step in this thread:

https://www.forum.simplymaya.com/show...ighlight=label

Mike also has a tut on layered shaders at his site, https://www.mtmckinley.net/ in the "other" section.