projects can set the desired launcher version

    via property 'launcher dependency'

ZmtLaunchPlugin.groovy
    uses project property 'launcherDependency'
        when adding dependency on launcher library
        if property is not found, latest version is used

src/main/groovy/de/zmt/gradle/ZmtLaunchPlugin.groovy

@@ -11,6 +11,8 @@ import org.gradle.api.file.DuplicatesStrategy
  * folder. It also adds start scripts for the launcher.
  */
 public class ZmtLaunchPlugin implements Plugin<Project> {
+    public static final def LAUNCHER_DEPENDENCY_PROPERTY_NAME = 'launcherDependency'
+
     private static final def MAIN_CLASS_NAME = 'de.zmt.Main'
     
     private static final def CONFIGURE = {
@@ -61,8 +63,15 @@ public class ZmtLaunchPlugin implements Plugin<Project> {
         // the launcher project is not present
         else {
             // add launcher dependency and make it an application
+            afterEvaluate {
+                def launcherDependency = project.properties.get(LAUNCHER_DEPENDENCY_PROPERTY_NAME)
+                // if not set by project, use latest
+                if (launcherDependency == null) {
+                    launcherDependency = 'de.zmt:zmt-launcher:latest.release'
+                }
                 project.dependencies {
-                runtime 'de.zmt:zmt-launcher:latest.release'
+                    runtime launcherDependency
+                }
             }
             configure(project, MAKE_APPLICATION)
         }