I guess you really can't do it with dynamicCall. I finally found how to do it. It was easier than I'd thought. With the installation of Qt comes a tool called dumpcpp. Its full path for me was C:\Qt\Qt5.1.0x86\5.1.0\msvc2012\bin\dumpcpp.exe (obviously depends on settings). You can just add the bin folder to your path to make it easier to use. Then I went into my project folder and executed this command :
dumpcpp -nometaobject {00062FFF-0000-0000-C000-000000000046} (the CLSID is just for the example, not the one I used)
It creates a header file, you can include it in the file where you're trying to use the COM Object.
In this file in my case there was two classes (IClassMeasurement and ClassMeasurement) in a namespace (MeasurementLib). Again, the names are not the real ones.
In your initial project file, you can call the desired function like this :
MeasurementLib::ClassMeasurement test; //Do not use IClassMeasurement, you only get write access violations
QVariant rangesVar;
int p1 = 0;
int p2 = 0;
int p3 = 0;
test.getRanges(p1,p2,p3,ranges);
QStringList ranges = ranges.toStringList();
Hopes that it helps someone !