I did use an air compressor with the 90 degree attachment but I did my second one with a very sharp screwdriver and carefully tapped it with a hammer. The secret is to sharpen the head of the flat screw driver so its sharp with an angle grinder and then you tap carefully parallel to the tunnel surface and use
some good pliers to you peel away the steel or flap it from side to side till you it comes off, you might have to cut some sections of it with a grinder to make it easier to stick the screwdriver into it and then use the pliers.
Then just use a cutting disc with small grinder to nip at it if you have to but otherwise the sharp driver head is enough to cut the mount off and when you remove the whole lot just use a grinder to smooth it. I did the same to other parts of the 1000 that where spot welded and have become quite good at it that it impresses me immensely :)