yes so it is ok for mct but as you note AY's site doesn't let you book it. never tried calling, but potentially you could try that and ask them to book. oddly if you did have a cancellation, AY's disruption tool on their site will allow you to book the b2b.

other strategies are book two one ways, or if you need a few nest one inside another so a HEL-AGP-HEL with a AGP-HEL-AGP nested inside. the AY app seems fairly robust so you shouldn't have an issue getting it to check in and issue a bp for the return of your b2b.