My logic says no.
Station A: Swipe, board.
Station B: Disembark, swipe, cost is calculated and deducted.
How will it determine the fare on a double swipe?
Your logic is almost correct in that it's not possible. The method is a bit off though. This is more how it would go down:
Station A: Swipe one time, go in. Pass card to next person, guard immediately tells you to GTFO. In the event that does not happen, or the entire army of guards at every station (TIA after all, they are there for a reason) are otherwise occupied, pass card to person outside the turnstile, alarm goes off on the second swipe, gate doesn't open and pandemonium ensues. Similar to what happens if you swipe in and out at the same station without swiping out somewhere else.
Station B: Police Station, I guess, if you don't have a good enough excuse at Station A.