I don't know if I got your question right.
I assume you want to build an Eclipse RCP application with tycho and use an JAR file from one of your plug-ins.
The simplest solution is then to create a new plug-in project from this jar by using the Plug-in from existing JAR Archives-Wizard.
If you have done this, you can add a dependency from this new plug-in to your existing plug-ins. Don't forget to export all packages of the library, by opening Manifest.mf and adding all packages in the Runtime tab.
To get this running with maven you have also to add a pom.xml file to the new Plug-in. This link help me a lot with maven tycho (http://codeandme.blogspot.de/p/tycho-articles.html).
Btw. if you don't need this library as plain JAR, you can also create directly a Plug-in project instead of first creating a JAR and then creating a Plug-in project.
