=============================== APEX CLASS ========================================

public with sharing class delete_me {

    public String varAttachmentParentID = 'test';

    public pagereference getGoToUploadPage(){

        PageReference tmp = Page.delete_me;
        tmp.getParameters().put('YOUR_KEY', varAttachmentParentID);
        tmp.setRedirect(true);
        return tmp;
    }
}



=============================== VISUALFORCE PAGE ========================================

<apex:page Controller="delete_me">

    <flow:interview
    	name="delete_me"
    	finishLocation="{!goToUploadPage}"
    />

</apex:page>