JavaFXPorts Multi-Dex Android Build

Question

I am porting a JavaFX application to Android using JavaFXPorts. However, assuming I understand this error correctly, I need to perform a multi-dex build. This is not surprising, since the project has many dependencies.

./gradlew :client:android
...
:client:dex[ant:java] Java Result: 2
 FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':client:dex'.
> UNEXPECTED TOP-LEVEL EXCEPTION:
  com.android.dex.DexException: Too many classes in --main-dex-list, main dex capacity exceeded
        at com.android.dx.command.dexer.Main.processAllFiles(Main.java:546)
        at com.android.dx.command.dexer.Main.runMultiDex(Main.java:366)
        at com.android.dx.command.dexer.Main.run(Main.java:275)
        at com.android.dx.command.dexer.Main.main(Main.java:245)
        at com.android.dx.command.Main.main(Main.java:106)


* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

I followed the instructions for configuring the multi-dex build, but it does not appear to be compatible with JavaFXPorts. Specifically, when I add this to my build.gradle:

compileSdkVersion 21
    buildToolsVersion "21.1.0"

    defaultConfig {
        ...
        minSdkVersion 14
        targetSdkVersion 21
        ...

        // Enabling multidex support.
        multiDexEnabled true
    }

I get the following error:

./gradlew :client:android

FAILURE: Build failed with an exception.

* Where:
Build file 'C:\Users\username\myproject\client\build.gradle' line: 67

* What went wrong:
A problem occurred evaluating root project 'client'.
> Could not find method compileSdkVersion() for arguments [21] on object of type org.javafxports.jfxmobile.plugin.android.AndroidExtension.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

For reference, my build.gradle is as follows:

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'org.javafxports:jfxmobile-plugin:1.0.8'
    }
}

apply plugin: 'base'

subprojects {
    apply plugin: 'scala'
    apply plugin: 'org.javafxports.jfxmobile'

    repositories {
        jcenter()
        mavenCentral()
    }

    dependencies {
        ...
    }

    mainClassName = "com.myproject.client.Main"

    jfxmobile {
        ios {
            forceLinkClasses = [ 'com.myproject.client.**.*' ]
        }

        android {
            // This does not work with JavaFXPorts
            /*compileSdkVersion 21
            buildToolsVersion "21.1.0"

            defaultConfig {
                minSdkVersion 14
                targetSdkVersion 21

                // Enabling multidex support.
                multiDexEnabled true
            }*/

            packagingOptions {
                pickFirst 'META-INF/LICENSE.txt'
                pickFirst 'META-INF/NOTICE.txt'
                pickFirst 'reference.conf'
                pickFirst 'rootdoc.txt'
            }
        }
    }
}

How can I configure a multi-dex build for a JavaFXPorts project?