You can use custom actions to achieve this.
Right click on the gallery and select Add event...
Select Swipeable Gallery > Frame tap event
Select Custom > Add custom action
In the custom action, have something like this:
var gallery = document.getElementById('gwd-swipegallery_1');
if (gallery.currentIndex == 1) {
gwd.actions.gwdPagedeck.goToPage('pagedeck', 'page1_1', 'none', 1000, 'linear', 'top');
} else if (gallery.currentIndex == 2) {
gwd.actions.gwdPagedeck.goToPage('pagedeck', 'page1_2', 'none', 1000, 'linear', 'top');
}
I've included my test file so you can check it out also.
Hope it helps.
San
Google Web Designer team