Well, there's his jacket. And really, he's tiny enough that she could probably just fit her whole mouth around his torso. So long as she was careful about it...

But he's unsurprisingly not a fan of the idea, and she doesn't yet appreciate the extent of the jam he's in (though once they get to the TARDIS, she might have a few words to say about the importance of efficiency in these circumstances). "Just an idea," she says. At least he's acquainted with it, now, so maybe if she does have to pick him up, he won't panic. "Do you want to climb back up now, or wait until we reach the end of the cars?"