You could easily do name a card triumph without a riffle cull, but this would not be impromtu.
If you are familiar with the perfect faro shuffle and the principle that 8 out faros returns order, you could go from a semingly random deck (say 4 or 5 out faros into the 8 faro sequence), have a card named and then continue to shuffle (the remaining number of out faros required to get back to order), cut to bring the named card to top and proceed with triumph as per your usual method.
You'd then get the kicker ending that the deck is in numerical order.
You could use a deck switch to ensure it feels impromptu.
Just a thought to tide you over til you find and learn the riffle cull.
