This is more than likely a stupid idea, but I'm trying to think of a reason why it wouldn't work.

If you were to connect a VFD's output to an isolating transformer (probably via a sine filter aswell), what is then stopping you from having switched loads on the secondary side of the transformer?
The transformer would mean the VFD outputs never suddenly go open circuit, but could the VFD handle the sudden surge current?

The reason I'm asking, is I've been looking at upgrading/replacing my rotary phase converter, and I'm intrigued by the newer digital options, especially since I found a picture of one that appears to include a bog standard VFD.
I'm thinking feed 240V single phase in (there are VFDs available in double KW figures that will convert 240V single in 240V three), then connect the output to a step-up transformer to get 415V.

Am I missing something?