I'm so clonesome I could cry...I suppose it is not that great, but I still like the silliness of it (doesn't it sound like "ewe and lambs"?).
I've got no idea what the lams refers to. (Haven't seen the film: please don't give spoilers. )
I don't think this would count as a spoiler, since the trailers for the film made/make it clear that (explanation below in beige, just in case you really know nothing about the plot):
MacGregor and Johansson are clones on the run. We are used to the expression "on the lam," but "lam" is also a verb with the same meaning - to escape or run away. Ergo, Ewan lams.