Taping is done by most beauty queens at pageants, according to a friend who was a former Miss USO and Miss New York City. When taping, one must bend forward and push everything up and to the center. If you have a lot of body fat, or if you're weight challenged, you can achieve great looking cleavage. I personally recommend the double bra trick. Use the smaller bra on the inside and stuff the larger, outer bra.
Corsets are great, but tricky.
Most women have wider hips, so most drag queen corsets must be tailored tighter at the waist. It helps if you have the breast forms sewed inside the cup of the corset. The foam mastectomy replacement pads are the best for such a corset. The expensive silicone forms are more useful as bra fill. Waste cinchers do give you a wasp waist and can really pull a svelte look together.