Disney express

[Disneypixie2015]

Hi, looking for some advice. Booked to go on the Eurostar direct from London and read about Disney express. I haven’t booked hotel yet, trying to decide between booking onsite or buying aps and staying offsite as we will be back in June. Anyway what I’m wondering is if I book onsite can I book Disney express one way. I’ve seen people say they’ve booked one way (homeward) when checking out through concierge.
Thanks