Maybe what you're after.
public List<Element> GetElementsWithThisParameter(Document doc, BuiltInParameter param)
{
ParameterValueProvider provider = new ParameterValueProvider(new ElementId((int)param));
FilterStringRule rule1 = new FilterStringRule(provider, new FilterStringEquals(), "", true);
ElementParameterFilter filter1 = new ElementParameterFilter(rule1, true);
return
(new FilteredElementCollector(doc))
.WherePasses(filter1)
.WhereElementIsNotElementType()
.ToElements() as List<Element>;
}
.WhereElementIsNotElementType() pretty sure that excludes element types.
hope it works.