Everything can be refashioned. Everything, even panties. I had a small handfull of thongs, that was "free gift with purchace" of some bras I once bought. Never used them. When I recently sorted out my wardrobe, they were unearthed and I decided to let an idea of mine come to life.
When I first saw these pictures on Pinterest, my thought was: "That woman is attaching a thong to her bra??"
Link to the picture as I don't think I am allowed to post it here: https://dk.pinterest.com/pin/222646775299791000/
Such a cleavage cover is a good idea. I don't feel the need to cover up completely, but a neckline can become too deep. And also I like layering my outfits, and with these I can add a layer without adding the bulk of a camisole.
I cut the back off of the panties.
Then I put on the cleavage cover-to-be and marked where to put snaps. And added those.
The sides of the cleavage cover is folded around the straps of the bra and you close the snaps. The lower edge is folded down and around bra edge. A proper tightfitting bra will be able to hold the edge of the cleavage cover in place.