I was just looking for around here, and it doesn't include trains heading southwards, for Preston northwards the only destination is Edinburgh (and Haymarket). Also doesn't include my local station so I've tried putting Lancaster as a start, and while there are trains from £5 each way under the terms and conditions it has :
3. Break of journey is not permitted, you can only go on the train we book for you.
So I take that to mean can't start/finish short even if on the correct train?
I also note that on a Saturday there is only one train in the 1700-2300 time window heading south from Edinburgh (to stations towards Preston), so for anyone wanting an advance on the 1811, then subject to availability this is one way to do it.