I like the mayo idea. Use the Japanese mayo and apply while on the grill. I might even be tempted to torch it a little for effect. Citrus (yuzu) likes the scorch. IMHO
The melded (not melted) mayo into the succulent pork might be bangin. The patty, with the mayo (egg), and the diced pickles (conichorn) on top might conjure images of tartar when you take a bite.