Best method for "painted" Jacket-layer?

I want to come up with some kind of quick and dirty template of some sort or another for a prim attachment that I could superimpose over the back of a jacket-layer garment (a leather jacket in this case) to show up either as "painting" directly onto the jacket's surface, or maybe appear like an old t-shirt or piece of canvas safety pinned to the jacket's back, a la how we used to rock it back in the eighties stylee. Any ideas about how to best proceed? I was thinking about using a regular shirt tattoo layer, since I've noticed those sometimes show up through jackets.. would this be simplest, or is there a better way?

Paint this into your actual 'jacket' texture. Orrrrr...you can create an alpha texture representing the patch, texture a prim with this, and attach it to your AVs back...

*shrugs*