Add to Local Maven Repo, then use it Gradle

Install downloaded jar file (here sqlserver jdbc driver) in local maven repository

mvn install:install-file -Dfile=sqljdbc41.jar -DgroupId=com.microsoft.sqlserver -DartifactId=sqljdbc4 -Dversion=4.1 -Dpackaging=jar

In gradle file add mavenLocal() and use the lib as normal maven dependency.