Believe it or not, stop really does mean stop.
It’s certainly not possible to map the Stop button to anything else with Encore DVD, and I don’t believe this is even possible to do in the DVD-Video format, with any DVD authoring tool.
If users are DVD-savvy, they’ll be able to bypass any menu requirement you may want in your DVD by using a title search to navigate timelines. However, for the non-savvy, you could create an timeline first in your project (Encore writes timelines in the order of their creation as titles on the DVD), and set its end action to your menu. That way, when a user stops the DVD, then hits play again, the timeline will play for a split second, then go to the menu.
Hope this is helpful,
Joe