Thanks Alexei, that gave me enough of a lead. This can easily be done with Presentations by turning the ScaleDivisions off and using an XTickLine in an Epilog option. The gauge is actually a Graphics expression inside a DynamicModule. So the following achieved the desired ticks on the gauge:
The only problem is that this exposes a flaw with ThermometerGauge. Whenever the first argument is a Dynamic[variable] the upper portion of the thermometer is not drawn! And on the ThermometerGauge Function page there is not a single example of using a Dynamic variable! Of course, we all know that thermometers can't be used as input devices so maybe it's not that bad.
As much as you can see from the answers to my question, there is no satisfactory solution. In any non-standard case one has to build a considerable part of the gauge himself. This we can do, however, also without the WRI gauge template.