Option available only for Residential or Mobile zones with multiple IPs allocated. To target a specific gIP allocated to your zone, use -gip-gip_name request parameter. 
curl "http://target.site" --proxy brd.superproxy.io:33335 --proxy-user brd-customer-<customer_id>-zone-<zone_name>-gip-us_7922_fl_hollywood_0:<zone_password>