How do I make sure that functions are not overloaded to the same name when they have different return types?

[koen-lyfo]

I'm working on a Javacard applet. I'm using Proguard because I have almost no memory on that card. I also optimize aggressively because of this. Proguard will overload functions, which is fine, but if an overloaded function has a different return type from another function, then the converter (which turns the JAR into something that the card understands) will throw an error.

I want proguard to overload functions, except when they have different return types.

My rules:

-verbose
-allowaccessmodification
-optimizeaggressively
-dontwarn java.lang.Class
-repackageclasses com.example
-optimizationpasses 10
-keepattributes Exceptions
-optimizations !code/simplification/arithmetic,!code/simplification/cast
-useuniqueclassmembernames

-keep public class com.example.MyApplet {
    public static void install(byte[], short, byte);
    public void process(javacard.framework.APDU);
    public void processToolkit(short);
    public void uninstall();
}

Below is an example. I'm concerned with the bottom functions:

public class MyApplet extends Applet implements ToolkitInterface, AppletEvent {
    byte[] timerIds = new byte[3];
    MyApplet() {}

    public void configureToolkit() {
        ToolkitRegistry toolkitRegistry = ToolkitRegistrySystem.getEntry();

       for(byte i = 0; i < (byte) timerIds.length; i++ {
            timerIds[i] = toolkitRegistry.allocateTimer();
        }

        toolkitRegistry.setEvent(EVENT_PROFILE_DOWNLOAD);
    }

    public static void install(byte[] bArray, short bOffset, byte bLength) {
        MyApplet applet = MyApplet();
        applet.register();
        applet.configureToolkit();
    }

    public void process(APDU apdu) {}

    public void processToolkit(short event) {
        switch(event)
            case EVENT_PROFILE_DOWNLOAD:
                for(byte i = 0; i < (byte) timerIds.length; i++ {
                    startTimer(timerIds[i], i);
                }
                break;
            case EVENT_TIMER_EXPIRATION:
                byte timerId = getTimerId();
                startTimer(timerId, (byte) 5);
                break;
            default:
                break;
        }
    }

    public void uninstall() {}

    // If these are not inlined, they will get the same name.
    // But they have different return types
    void startTimer(byte timerId, byte seconds) {
         // impl
    }

    byte getTimerId() {
        // impl
    }
}

Most of the time these types of functions are inlined. But assume that for some reason these functions cannot be inlined.