I think a callback necessary, but I'm not convinced should be part of getSortedElements, which isn't specifically to do with paging..

The namefilterlo/namefilterhigh handling that getSortedElements performs doesn't apply to your variety, although you use the namefilter in your own context. 
The sorting does apply, but you can reuse cSort in your own callback implementation.

getElementsPaged seems to be more logical place and leave getSortedElements untouched.