How can I adapt a wall outlet to suface mount conduit?
There are collar boxes available that have conduit KO's (knockouts). Just install one on top of the existing device box and run your conduit. 



This one is even better as it has more volume:



Brand: Steel City, Part number:531511234UB

Here is a raised device cover to be used with the 4x4 box shown. They can be had in any number of different configurations.