I'm in the process of converting an old mountain bike frame into a fixed gear. I have Dremeled the canty mounts off of the steel fork and I'm in the process of filing down the welds. There are vent holes about 2mm diameter in the fork blades. Since I don't have easy access to welding equipment, what's the easiest way of adequately filling in the holes. Will Bondo stay put in such a small hole that has no backing?