A soul sleep adherent would simply say that in the Matthew 14:26-27 passage, the disciples thought Jesus was a phantasma, a Greek term for spirit appearances or apparitions, based on their understandable superstition related to a disembodied spirit from someone who had drowned and haunted the water. More likely, they may thought that an evil spirit (non human) tried to deceive them into thinking it was Jesus, since they know that Jesus was still alive.
Note also that Jesus simply said "It is I", without acknowledging that dead people's spirit can roam and haunt. There is also no place in the Gospels that Jesus implied that human spirits waiting for resurrection are free to roam among the living. Also, the main point of the passage is to show how Jesus is Lord over all creation.
Similarly, soul sleep adherents would read Luke 24:36-39 as Jesus's assuring the disciples who at that point were still doubtful of the resurrection and who were instead frightened because of the same superstition as in Matt 14:26-27 (a non-human evil spirit trying to deceive them). The word used was pneuma but at least one commentator said the usage is parallel to phantasma in Matt 14:26-27. But just because Jesus was using a word that came to the disciples' superstitious mind upon seeing Jesus's glorified body should it be taken as support for waking spirit in the intermediate state?
Christians of all stripes, soul sleep adherents included, interpret the Luke passage to prove Jesus's resurrection as well as as a preview of the bodily nature of the glorified bodies we will also have at our resurrection, especially against the growing Gnostic threat denying the goodness of the body.
Conclusion: Given the main import of both passages, soul sleep adherents would consider both usage of phantasma / pneuma as simply the narrators portraying the disciples' superstition and that they are too fleeting / irrelevant to be used as support against their position.