There is currently a LoRA that does a similar effect, but noticeably with more anime/animation style and smaller breasts.
This is modeled on larger breasted examples. A strength of 0.5-1 works well. Some models don't seem to handle this that well, but most I tested, real or animated, worked well.
Keyword: paislash
Others: strap between breasts, seatbelt between breasts
Description
Initial release - it takes a little fiddling to make the strap not look otherworldly, but I was able to get decent results, refer to examples.