Actually, you should be able to place the drivers into common/lib only once and from then on they should get used. (This is what I do.)
By the way, did you place those drives into yourp roject in Eclipse? Why? Are you coding directly to them or are you coding to the JDBC interface? If the latter, the project does not need the drivers. (I never add the drivers to anyt of my projects, nor do I add them to Maven dependencies.)