Assuming you have babble already...
Turn on power.
Go to bank and get $10,000 points for each player.
When you return to the tranzit bus depot, the bus driver will say new route activated and he will have very different lines.
After this point I have not tried, but it's what I hope you all can test with me:
The first glowing bowling pin is green in the bowling alley. So try drinking the speed cola perk your second time around. Go to the bowling alley and see if the pin changes color.
Another possibility is water, and it may be the step used prior to bowling alley. The driver talks about water a lot when repaired, and your characters also discuss a tree house in the woods.
Give it a shot! Let's get to the next Easter egg!