In our organization we found a database table that has the Zip code and it's corresponding city, state, long and lat info. We can then pull this into Qlik via the loadscript and map data using the Lat/Long info. Is that something that could work for you, rather than a plugin that translates a zip to coordinates?
We have used a similar process that Charles Spencer described. We have a table with all the zip codes and their corresponding latitude and longitude. That table also includes information about the city, states, etc. There are several sources of zip code information that I found. Some are less accurate than others because they will group multiple zip codes into one latitude and longitude unless you pay for the more accurate version. However, census.gov has a free set of information that is more accurate.
Here is the official site with more accurate, free data:
