How can I reliably crimp aluminum ferrules without a specialized tool?
Just crush the thing with any tool you have around.

I googled the phrase "crimping aluminum sleeve without tool" to find examples of a child using pliers to get this done:
https://www.youtube.com/watch?v=rMJETUcYNxg

If you can use a big vise to crush them down, that's probably the most 'controlled' way.  Otherwise, use pliers, or get a hammer and chisel and dent the sleeve at two or three points with the chisel.  

Plan on destroying one or two sleeves first just to get the technique down.  Then, once you have one that looks right, really try to rip the wires out (to verify that you have a good internal connection).