Load class instances over SPARQL endpoint?

[KonradHoeffner]

I have select fields that should contain all instances of a certain class and there are too many of them to fit elegantly into form.html. Is there a way to get RDForm to automatically load the instances over SPARQL?

[KonradHoeffner]

I tried to load it myself and inject it inside the input element of form.html but unfortunately that didn't work because it was not in the DOM yet. Is there a recommended way to achieve this?