When I do exhibition stands, often, I have an image in background (material 00) and a logo with alpha (material 01). I can move move or scale each other easily. I know we can do it with BP but it's so easy with stacking materials.
As a fellow exhibition stand renderer, using corona shouldn't stand in the way to do that very easily and controlled. My technique I use all the time is with a plane object at a distance of 0.05cm in front of the wall and apply your alpha material. If you put that plane in a null object with the 0.05cm already applied to the null, you can even quickly snap the null to the wall and be sure the distance is kept. You can instance that null for quickly scale or reposition all logos at the same time.
For the plane, also don't forget to add a compositing tag with shadows disabled so you will never see that it is actually floating in front of the wall.
For round surfaces with stacking I select polygons, split and offset with extrude to get the floating geometry.
just a tip...