Allan, I was thinking of the small force that was sent out at the end of the Peninsular War. War of 1812 - Washington, New Orleans etc..
Many of those just made it back to Belgium in time to take part in Waterloo. Absolutely no reason to presume that Stephen Freer / Friar / Frier was one but it's a fascinating part of history.
The story of Harry Smith (who ended up a General, having married a Spanish lady during the Peninsular War) or Johnny Kincaid (both Rifle Brigade) give a huge amount of background and so (please don't discount her) does Georgette Heyer.
General Sir Brian Horrocks always said that her novel The Infamous Army gave a clearer picture of the Battle of Waterloo that most military tomes
Added: in case anyone is interested, the books I was referring to are: The Autobiography of Lieutenant-General Sir Harry Smith, Baronet of Aliwal on the Sutlej, and Tales of the Rifle Brigade: "Adventures in the Rifle Brigade" AND "Random Shots from a Rifleman" by Sir John Kincaid
Sorry TKEJ, I'm digressing, I do hope the Stephn Freer on the Waterloo Medal list turns out to be yours. I've no idea how to search the Royal Hospital records to see if he would match up, but if nobody turns up here with the knowledge, it might be worth asking for that expertise on the Armed Forces Board - there are a lot of very knowledgeable people there. If you do, refer back to this post so nobody is duplicating.