Mmm, interesting. Apparently there was/is a scam whereby if you are travelling from A to D, passing via B and C on the way, some people bought separate tickets from A to B and from C to D, then used the A to B ticket to get through the barriers at A and the C to D ticket to get through the barriers at D. Gets through the barriers, though if you have your non-ticket checked anywhere between B and C, you're hosed. (See here, for instance.) I think your plan is, effectively, a variant on that and an exceptionally cunning one. Still prohibited, of course.