Android : Sharing a service between applications

Say I have a generic service (not an Android service) that I wish to share between applications

package com.projects.services.someservice

class SomeService {
    public SomeService () {}

    public void start() { /*start service*/ };

    public void stop() { /*stop service*/ }

    // other methods...
}

Now say I have two Android application projects (com.projects.app1 and com.projects.app2) which each have their own instance of SomeService. How can I share one instance of the service between the applications? Would I have to refactor the service into an android service and initialise it independently? Or can I pass one application's instance to the other.

I am facing a situation where I start app2 from app1 via an Intent:

// called within an activity in app1
Intent i = getPackageManager().getLaunchIntentForPackage("com.projects.app2");
i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(i);

What are my options?