‘Switch’ a sweet story despite contrivances

You have to overlook a whole lot of guff in order to enjoy the slight but pleasurable entertainment of “The Switch.”

You have to believe that a woman named Kassie, who looks like Jennifer Aniston, would have so much trouble finding a romantic partner in New York City that she decides to go the artificial-insemination route in order to have a child.

You have to swallow the fact that her best friend Wally (Jason Bateman), who is obviously in love with her, has never tried to kick things up a notch since they went out on a couple of dates and fell into a best-pals routine.

And you have to try to ignore the implausibility of a drunken Wally accidentally destroying Kassie’s donor sperm and replacing it with his own, then completely forgetting his actions until seven years later, when Kassie returns to New York with her son Sebastian (Thomas Robinson).

Get past the pile of contrivances, though, and “The Switch” is a surprisingly sweet, tender story of a man paralyzed by unrequited love but motivated by parenthood to break free of his stasis.

Directors Josh Gordon and Will Speck (“Blades of Glory”) and screenwriter Alan Loeb have jettisoned much of Jeffrey Eugenides’ original short story “Baster,” primarily using the switcheroo as the basis of a crowd-pleasing, soft-edged romantic comedy.

“The Switch” heroically tests your patience, because it’s the kind of movie in which you know “every single thing” that is going to happen five minutes into the story.

But Bateman, playing a slightly darker variation of his familiar comic persona, injects a layer of genuine pathos into Wally, and he delivers the laughs when the movie needs them – such as during the big change-up scene, tricky business cleverly handled by the filmmakers within the confines of a PG-13 rating.

Aniston has a harder role – Kassie is more sketch than fully realized character – and the movie suffers whenever you stop to think about her behavior and its motivations.

“The Switch” benefits greatly from comic supporting turns by Jeff Goldblum and Juliette Lewis as the leads’ respective best friends.

But the movie ultimately is Bateman’s show to carry, and he manages well, even though it is in dire need of a few plot wrinkles or twists – something to give the awfully slight picture a little more weight.