Ficus have pretty resilient bark. I'd tend to agree with Mellow Mullet, that carefully cutting out the scar is a good option that heals faster than the wire marks. I'd describe it as carefully shaving down the area immediately surrounding the scar, which will expose a layer of the cambium. This should heal up fairly easily with much reduced visual scarring. I would personally use an exacto knife with a curved blade. You can choose from several appropriate blades for delicate work, such as one of these:
Shop X-Acto Blade - No. 11, Pkg of 15, Safety Dispenser, Stainless Steel at Blick. Find everything you need for your next creative project online.
www.dickblick.com
Just be very careful using these, they can cut very deeply, but they give you excellent control.