How to change property without exposing the property sheet

Question

I have the CLSID of the property pages of an encoder. I retrieved this by querying the filter for IID_ISpecifyPropertyPages.

hr = pHauppaugeSienaEncoder->QueryInterface(IID_ISpecifyPropertyPages, (void **)&pProp);

I also have the array of IUnknown.

But how do I get access to the properties to be able to change the values? How can use these CLSIDs?