Hi Dr Phil -
Unfortunately you will have to keep dreaming about an Analyser Vario. The circuitry would indeed be complex, as would the software, because the unit would have to monitor the light level from the tubes and subtract any changes from the readings from the baseboard sensor, because otherwise the sensor would interpret those changes incorrectly as changes in negative density. It would also need an absolute reference for tube light level, so it could work out any necessary change required during the exposure. It all gets a bit difficult as you can appreciate I'm sure! The likely market for the device would not recover its development costs I don't think.
So long as you keep the tubes lit as much as possible to minimise the likelihood of output variations, you should find a standard Analyser / ZoneMaster will work OK. I know of at least one customer using a ZoneMaster together with a Vario successfully with a DeVere 10x8 cold light.