THEFERMANATOR
God
We know that fuel, even with a 100 : 1 mix is different chemically than just straight fuel. There are ways to measure it. Without really thinking about it too much, I think a sensor hooked to a microprocessor that measures the viscosity of the fuel several hundred times a second as it flows past might work. (I think that fuel with oil in it would have a different viscosity index than fuel without oil in it). You just have to monitor the thickness of the fuel. If it falls below a set parameter it would send a signal to a solenoid that would switch a valve to a different tank filled with premix in it and sound an alarm. The problem of course is writting the program. The rest is just basic mechanical stuff.
Personally that is to overdone for me. It only takes a few extra minutes to use a mixing bottle and KNOW the oil is in it. Unfortunately for the DFI guys, this won't work.