I have indeed worked with this issue.
In the diff amp configuration with lots of global series feedback the substrate tends to be bootstrapped pretty effectively just by letting it float (which btw is Toshiba's explicit recommendation in the (obsolete) 2SK389 and 2SJ109 datatsheets).
When used single-ended and paralled the same thing will happen with series feedback, and even very local feedback (a resistor in the source(s) for example >> 1/gm) will help a lot to reduce input C.
In other configurations with those parts, such as the popular voltage follower where the upper source follower is supplied current by the lower device's drain, with usually each part having a small R in series with the source to limit the current in the lower to less than Idss and in the upper to provide a matched compensating output voltage offset, a significant fraction of the input capacitance comes from the substrate. It is then useful to drive the substrate actively. However, the breakdown voltage has to be determined. It appears that the Toshiba parts have back-to-back isolation diffusions/implants, as I get no diode conduction from the substrate to any of the other electrodes, and the breakdown voltage is pretty high (>100V for what I tested). So those I tested would be difficult to fry. There is no specification though, so YMMV.
I have not played yet with the LIS parts, so I don't know for sure what they are doing besides the interdigitated structure, but when I spoke to them after the release of their LSK170 and they mentioned the dual coming up, I suggested that they provide a substrate connection and cited why. Either the guy I spoke to didn't know that they were going to anyway, or they changed their minds, as he told me there would not be one. But lo and behold there it is, and good thing for it.