Area chart with y axis value offset

[mulgurul]

Hi

First thanks for a really nice Graph package, great work.

I'm investigating if I could use the area chart for an application. The area graph is a bit special, as it deals with dB values ranging from -20 to -120 (could also be 0, but data will seldom be > -20)
Something like this example from another application:

The best thing would be if I could set the Y axis to have an offset on -120 instead of using 0/zero for calculating the coloured area, so if a series value is -60 it would be filled from -60 down to -120. I might fear that this is not possible?

I've also tried to make an extra series where each Y value from real data series is subtracted from -120 and then stack and hide the "offset" series by making it background color. This is not quite optimal. I also need to have several data series in the chart, which might not be possible with this approach.

Have anyone some better suggestions or can point me to a property making this scenario possible?

Help highly appreciated.

Best regards, Peter from Denmark