electives are your 4th year of med school. usually subspecialties or areas you are interested in for residency to get a real "taste". you are basically treated as a 1st year resident so you get a good idea of what its really like (during 3rd year you are focused on learning how to write a note, take histories, etc)
would a 4 week elective help you getting a residency? probably not much since you would be learning an entire system by learing how to write, present cases, the drugs, treatment plans etc.. so it would be difficult to impress an attending enough to get an recommendation because you will seem clueless for a few weeks (the img's i've seen usually take 2-3 weeks to get in rythm). also any programs that require US clinical experience usually want more than 4 weeks so it will not help there either.
what you could do is after graduation there get a few observerships in the US. an observership is a rotation but you aren't allowed to have direct patient contact (do procedures). what it will do is get you used to the system and after you learn the set up you can get a few letters of recommendation to add to your application. if you get the first aid CSA book there is a list in the back of hospitals that allow observerships