Shall we go First Class?
In the UK 1st Class Travel now has some nice perks. OK getting a seat isn't what I was thinking exactly, but often drinks and food is included. It costs a bit more of course but I think I'm worth it. The great news is that the '1st Class' bit doesn't always appear on the receipt, just the ticket. So unless your claim is going to be checked by somebody with a mastermind brain for rail fares it’s an easy upgrade.
This one is not always easy to catch, but those that do this regularly often can't help but tell their peers, bragging about how they travel in 1st Class. A simple solution is to enforce a copy of the receipt with the ticket so that the authoriser can see both.