Differential controller for different sensed variables

[afool]

I need a dehumidification coil to turn on whenever the difference between dewpoint and drybulb temperature is greater than 10°. However, the differential controller in ApacheHVAC seems to automatically assume that both sensed variables are the same (i.e. dewpoint temp at two different locations or drybulb temp at two different locations) but cannot handle dewpoint temp vs drybulb temp at the same location. Is there another way to accomplish what I need?