I have tried the apokyn pen and it was a flop imho as far as a rescue medicine; however, I bet that 2 or 3 mg of Dexedrine in the pen format would do an EXCELLENT "rescue job". I'd bet that it would pick you up in 2 seconds flat.
What i did notice that i think is significant is that i don't go off like a lighbulb when i'm taking dex. I make it to the grocery store about once a week and used to find myself dragging behind the cart, in an "instant severe off" sitation. Some times I had to get assistance just to make it out to my car. This has never happened with concommitant dex usage. IT definitely prolongs the on time and dosen't let you "crash", there is some reserve there that allows you to carry on where you would normally go off. I think that dex would be very helpful in situations when you don't know how long you will be tied up somewhere, and you are past the point where another tablet or two of sinemet just doesn't do it.