Fill glass about 3/4 full with chilled club soda (no salt added). Shake in a few drops of phosphoric acid. Briskly stir-in flavoring with a spoon. Add ice.
Phosphoric acid, now frowned upon by nutritionists, is hard to find these days, but is an additive in many soft drinks.
The nonalcoholic Rickey was mentioned in Glenn Miller's 1942 hit Juke Box Saturday Night.
Why not include instructions on how to roll a fag?