This answer notes that the Chayei Adam knew of (and approved of) French Jews who would wear tzitziot on their waistcoats. However, this section of the Wikipedia article shows that the waistcoats worn in the Chayei Adam's days were significantly different in their form than our modern ones.
Here are images of the waistcoats of the Chayei Adam's period:
And the modern era:
Please note that these garments would still need to be split most of the way up the back to have 4 corners, AFAIK.
Are our modern waistcoats chayav (or at least accepting of) tzitzit?