Just came up with a new technic, it sounds kinda hard but if you can do the pass its very easy the pass would bring the selected card to top but with this technic you can do the normal pass and get the selected card to bottom.Although it requires a lot of practice to do it very fast.
so here we go
You get in the position to do the pass , same handling and mechanics but instead of moving the selected card to top just when you do the pass you steal the card with your pinkie its very hard to explain but let me try to get more into it

you are in position to do the pass your pinkie is over the selected card so if you do a normal pass it will bring the card to the top but instead of doing a normal pass bringing the card to top while doing the pass slide down the selected card and complete the pass what it does it brings the selected card to the bottom.
I donno how to say it but once you are in position to do the pass, slide down the selected card with pinkie and complete the pass.

Although I think having break below the selection and doing normal Pass is simpler to bring the selection to the bottom, HypnoticQueen's idea inspired me a nice way to reverse the selection in the middle of the deck.

Do as HypnoticQueen explains but reverse the upper half and the selection, then Half Pass the reversed packet except the selection.

Thanks for the inspiration.

Hideo Kato