I have been meaning to post this, and a recent thread on this got me off my butt. I stumbled onto a very good no-tape, reusable, cleavage maker that cost pennies.
I was in a big box hardware store looking for gasket material and lucked upon an employee that actually knew something. He showed me the expensive little packages of about 4 inch square, and then said I could buy huge sheets of material from the rolls of shower pan liner. For about $6, I bought one foot off of a 4 foot wide roll.
My project used a tiny amount, and then serendipity! Maybe I could use this very strong, synthetic rubber material in a bra instead of those flimsy, sticky nubra thingies. After some experimentation, I developed a cleavage enhancer that produced very satisfying results, as shown in the first picture.
The second photo shows how it is made, with some variations. The general idea is to cut out a strap that goes from under one arm to under the other. Be sure to make it long enough with a lot of surface area on the sides of your torso. Then cut out a dip in front where the cleavage will be. There are lots of options, but I suggest taking your favorite bra (mine was a push up) and cutting the dip to match the shape of the bra. Then fit the strap under the bra, and holding the lower edge of the strap, pull your breast into the cleavage you want. Insert pads, socks, breastforms, or whatever you use between the strap and the bra and you are set to go.
I also experimented with some braless variations, such as the one with the elastic strap attached. (The elastic only holds it in place and does not need to be very tight at all.) The third photo is just the strap under my top. I don't have enough flesh to make it look natural, but at home I do enjoy looking down from the computer and seeing small breasts and nipples under my top.
I like these a lot. No glue, no tape, no red marks, and with enough pushing and pulling, some very impressive cleavage. One caveat is that the material is, of course, impermeable, so moisture collects under it when you are warm. This reduces the friction, and you can find your cleavage slowly slipping away!
Have fun,
Liz