Here is the classic manner of performing this: The card is chosen, remembered, and replaced in the deck. It is controlled to either the top or bottom and palmed as the deck is handed to the spectator for shuffling. (Note that it is the SPECTATOR who shuffles the deck.) Afterward, when the deck is returned to the magician, the palmed card is added.
You can't beat the fairness of this sequence!
Having a card returned and then shuffling the deck yourself is not as clean.
There is, however, another way: When the card is peeked, crimp its corner, then hand the deck to the spectator to shuffle. You can find locate the card quite easily when the deck is returned to you. If you want to have the chosen card returned to a spread, it's an easy matter to crimp the inner right corner (hidden beneath the upper right hand spread of cards) with your right second or third fingers. Then square the cards and hand them out for shuffling.