Certainly - did this on mine - same setup as you, Mk2 DL1 and Dash4.
I created a user-defined channel I called "GaugeWarning" with the following definition:
((VAR_0010>5000) and (VAR_0200<1.5))
Where VAR_0010 is RPM and VAR_0200 is oil pressure (in bar). This, naturally, goes to a value of "1" when oil pressure is below 1.5 bar with RPM>5000.
Then you just have to set a warning on this using the Maximum value (maybe set to 0.
... probably set Minimum to -1, so it won't be triggered.
On the downside, unlike the normal direct input analogs, when the warning is flashed, you won't see the actual oil pressure value, just the bit of "1"...
That said, come to think of it, if you revise the calculation to:
(VAR_0010>1500)*VAR_0200*(VAR_0200<2)
You might be able to actually see the value if you wish... This would show the pressure value, but only if it's below 2.0 and RPM is over 1500.
However you'd have to config it as a max warning - as it'd normally be 0, so with a max warning value of, for example, 0.1, you should see the value displayed.
If you are concerned about seeing the value then.
I'd also recommend setting a max rate of change of some value, or smoothing, to avoid flickering messaging... have run into a bit of this kind of issue myself with dash warnings if you're running close to the limits... can be very annoying when the message keeps coming back just due to noisy signals/sensors...
Hope that helps...