WLP005 is an English style yeast, and in general, English yeasts tend to flocculate out very quickly and they tend to attenuate less than most other yeasts. As such, rousing the yeast is a very good idea but might not work. It's worth a try though. You could also warm it up even more, maybe to 22 C. You could also try adding a starter of a more highly attenuating yeast such as WLP001 or US-05 to get it rocking again. If you try this, it must be a vigorous starter -- if you only add a pack of yeast and skip making a starter with the new yeast, it probably wouldn't do a darn thing. But a vigorous starter with a more highly attenuative yeast is likely to get it going again. Then wait a couple weeks and hope for the best.