[LABride]

Here's what the Unofficial Guide says about a short cut:

...go to the end of Main St and turn left to The Crystal Palace. In front of the restaurant is a bridge that provides a shortcut to Adventureland. Stake out a position at the barrier rope. When the rope, drops move as fast as you can and cross the bridge to Adventureland.
Just past the first group of building on your right, roughly across from the Swiss Family Treehouse, is a small passageway containing rest rooms and phones. Easy to overlook, it connects Adventureland to Frontierland. Go through the passageway into Frontierland and take a hard left. As you emerge along the waterfront, SM is straight ahead.