commercial boost converters normally have voltage feedback and this makes it difficult to use them as I would want to. If you have to go inside and mess about with the signals to the pwm then you are probably into more difficult territory than building your own unless you are lucky to have the commercial circuit diagram.
That little thing you linked to would not really be suitable.
Someone here is playing with a Zahn converter, maybe you could find the details, it seems to have some promise.
You could manage something with a variac but it becomes messy with 3 phase and you need to seriously think about the frequency limitations. A tracking scheme would have to be very slow to obtain a reasonable brush life.
Flux