The hot air station might have a chance, but generally electronics equipment doesn't have the oomph for that sort of thing. Soldering only works if you get the metal hot enough to melt solder, and the very nature of a radiator is going to be spreading out the heat you add to the area quite rapidly.
The usual approach is to treat it much like a plumbing job. Brush the metal clean, acid flux, high-lead solder and gas torch, followed by cleaning again. That's after draining and removing the radiator, of course.
In your case, since you're planning to replace it anyway, I'd suggest trying JB Weld or an equivalent.