How can I use FVTool to view cascaded CIC and fractional rate converter?

I've used FVTool before to view the overall frequency response of cascaded CIC and CIC compensation filters in a down sampler. I'm now trying to do something similar but the CIC compensation filter has a fractional rate change, specifically 2/3. FVTool gives the following error:

I've tried changing the downsample factor to 1 (so the sample rate is no longer 2/3 but 2) hoping that the filter has the same coefficients. However, this time I get another error message:

All I want to do is view the combined response ... and these are them shown separately

Any advice would be gratefully received. PD