I normally do the same thing but recently had to put up a tv on a metal stud plasterboard wall.
In the end I had to buy these fittings.
Grip It
They aren't cheap but they worked better than I had anticipated. The downside is that you have to drill big holes for each fitting and you may need to buy bolts that are longer than the ones supplied.
They aren't ideal for every situation though. If you are fixing something that is narrow, you might be able to see the fitting.
I would recommend them though.
