Let me first preface this by saying, i am not qualified to be the definitive end all of answers. I am only a hobbyist who happens to like playing with things that can kill me. Safety is your responsibility.
You could connect the mains to the secondary as opposed to the primary and it works great, tried it and done it. But it usually only gives out a couple volts of AC, at least it is isolated AC. Then I also tried taking that 2 volts and putting it back through which also worked, gave me 120 volts AC back out.
Now here are the problems, sorry nothing is perfect, there may be issues with the ability to supply current and that is realy try as you go method. But also one end of the high volt side is connected to the transformer chassis, so then you would have 120V AC on a massive hunk of metal. You can work around this, drill out the rivet or just cover it but it does pose a safety risk.
Ultimately, will it work for your purpose? Up to you to do your own testing and see, just please keep safety in mind. These are not child's toys even without the 2000 VAC.