Damn lintels and curtain rod support, an AB mixture might do it but then you have to find a way keeping the baton tight against the wall while the mixture sets.
A decent drill and a couple of decent SDS masonry bits will do it and persevere, you only need 50mm not including thickness of baton but damn those 50mm can be hard won.
Don't forget to check where the rod's support brackets are being fixed on the baton as you might need to off set your baton fixings.
For me, curtain rods and lintels, I just break out big Girtha and a decent bit, problem solved.
Good luck.