I have a suggestion. With your model simply make a copy of it. After doing such, take the copy and cut out the area of the surface of the bottle that your trans map is applied. After doing this, and make sure you only cut out the surface area with the trans map on it!, Loop cut around the cut area that you made around the trans map. Now delete the top and bottom remaining parts of the bottle. Now select the faces on the cut selection that still has the trans map on it. Now zoom in, and multi. extrude the faces slightly, just barely. And once this is done. un-select the faces. Zoom back out, and drag it over to where the label should be on the original bottle which just re-apply the glass material to. Now it should apeare as the label is on the bottle. Make sure that the trans map is set so that it is completely transparent. Now when rendering, make sure that you make sure that the "new label mesh" cannot cast shadows.
Any way have fun and I hope my write up helps. If you need any further help or explanation just ask.
Nate/ncl32