One option might be--if you have the available credit limit--to buy two (or even three) Amtrak tickets: one for the train you think you'll make, and then one or two for later itineraries.
Amtrak tickets are refundable for (IIRC) a couple of days after the scheduled travel dates, so all you'd have to do is, after arriving home, call and cancel the one(s) you didn't use. (IIRC, you can't cancel on the website after the scheduled travel date--you have to call--but you can still get a refund.)
This way, you can still lock in the low-bucket price and protect yourself against price increases. You just have to float the funds on your card until you can get the refund.