More likely to induce corrosion is the bar in contact with fresh concrete. You will passivate the existing bar where it comes into contact with fresh concrete, with presumably some electrically connected bar that is not passivated that is not prone to corrosion. I'd suggest adding a zinc anode tied to the exposed bar. Someone can correct me on this, but since you have a (presumably) smaller area of stainless compared to the area of black bar, galvanic coupling of the two isn't a big concern. Certainly can't hurt to isoalte them though, I'd probably use zip ties or a polymer twine instead of metal ties.

Galvanic corrosion shouldn't be a problem, but you want the repair to outlast you, so don't rely on "shouldn't". I second canwesteng & say use some kind of plastic ties. The mesh isn't heavy & won't be difficult to hang so isolate it completely.