When I do it I spread the cards from right hand to left.
Thus when the person selects their card I have the majority of the deck lodged between the fleshy bit of my thumb & index finger as in dealers grip.
My 1st & 2nd finger which are underneath the deck kinda scrape at the cards, sometimes using my nails so I can detect the very bottom card & once I'm sure I have the bottom card only I push it toward that fleshy bit of my hand which gives it something to buckle against.
For me this bit is the problem as this card inevitably push too far to the right & a small amount out from the spread.
I have by this point seperated the cards so that the selected card is on the top of the right hand pile. Then as I would say "this card" I bring my left hand over with the rest of the cards which are still in a ribbon spread state & take their selected card while at the same time pushing the bottom card over underneath.
To push the bottom card over I just use the 1st & 2nd fingers which have buckled it & then grab it with my left 3rd finger.
I then tap the left hand pile on top & on the side to square up thus hiding any inconsistancies. Oh & I make sure the deck is kept very angled down to hide those underneath movements.
As I said above I can do this fairly well bar the one problem of the buckled card pushing to the right but I'm not 100% on it which is why I have never used it bar on my kids who immediatly spotted it
