You can always access International Gateway when Future World opens at 9am. There's a chance World Showcase will be roped off to the right toward France, but you'll always be able to at least get from Future World to International Gateway and vice versa.
There's a couple of tours in World Showcase that operate when Future World is open but before World Showcase is (Backstage Magic and Segway).
We stay at BWV frequently and have never had a problem doing this. We've done the enter through IG to get to monorail trick before. I don't know that it's really faster than just waiting for the bus to MK if that's where you're going.