It's not a good idea to put a transformer on the output of a VFD. Transformers are designed to work on one frequency. When you change the frequency, you change the interaction of the steel laminations to the coil windings. The VFD output is also extremely rich in harmonics. The end result is usually a significant increase in heat in the transformer which causes rapid deterioration of the transformer winding insulation, followed by a short between windings and the probable destruction of the VFD output transistors. There are special custom made transformers designed for using below VFDs, but I doubt you can find one.
As mentioned above, check to see if your motor is dual voltage, which solves the problem anyway. If not, you could find a 480V VFD and put the transformer on the line side. A few 480V VFDs will not accept 1 phase input, but most will. Unfortunately, it will require that you double the size of the VFD, but then again, 1HP is usually the smallest 480V VFD you can buy anyway.