Best way for mirrored edging on canvas wrap prints ?

[KumsaJack]

I use GIMP extensively, and it's the front end for printing with Turboprint. Lately, I've been doing canvas wraps, and these require mirrored edges.

I can do them manually, but that's very slow. I've looked for a GIMP tool, but can't find a match up for the process.

I've attached an example of one that was done by select/paste/transform on each edge.

Thanks for any shared experience