I put a curtain pole up over some french doors and found that a steel lintel meant I couldn't drill deep enough. The solution was to cut two pieces of wood about 10mm thick and 75mm x 150mm so that the pole fittings could be fixed to the wood and the wood fixed to the wall below the lintel at the sides. IOW using the wood to displace the wall fixings.
Corners bevelled and painted, looks fine and they're behind the curtains anyway.