I have a set of drivers that are just slightly oversize. If I strip out a grub screw, or any screw for that matter, these will almost always pull it out. And since I have another set of drivers, this is all I used these for. However, these are made in china drivers, so my oversize may be undersize on the next batch. You can never tell with made in china.
If you have a Good set of drivers (not the cheap L drivers), you can try to put the driver in and cock it at an angle and turn. I would add a little heat as well just for good measure. Sometimes, these can be a pain. If this doesn't work though, a 1.5mm left hand drill bit will be about the only option if it's completely rounded. I have also used an old torx driver that I didn't care about and hammered it in to remove these.