I want to but an advance from Ashford (Kent) to Manchester tomorrow(Monday) using HS1 and then travelling on the 12:20 from Euston. I've tried a couple of booking engines but none offer this train with Advance tickets (as it is never the fastest with the standard connection times) but I wish travel specifically on the 12:20. Is there a tweak (forcing a longer connection time in London, for instance) which would show this train? My only other option is to buy separate tickets for each leg but this considerably more expensive.