I was told that the French military archives in Paris has the records for soldiers of the Seven Years War, but they aren't on microfilm and they don't photocopy the records. They also don't look up the records themselves, you need to hire a private researcher to look up the records and hand copy the information they contain. The archive can recommend a reputable researcher. Here is a short cut link to the website of the French military archives: http://www.afg-2000.org/manuel_genealogie/armee/archives_militaires.html#TERREhttp://www.afg-2000.org/manuel_genealogie/armee/archives_militaires.html#TERRE
This is what I was told about the records of soldiers of the Seven Year War, perhaps the Napolionic War records are in the same situation. I know if your ancestor was still alive in the late 1830's (I think), he might have received a Medal of St. Helene. It was awarded to Napoleon soldiers who where still alive at the time the medal was issued and who could prove their service. Also probably only to those still residing in France.
Let me know if you learn anything of these records.It's been a few years since the person who told me about the records, had gone to the archives. Perhaps now they are on microfilm, where they ought to be.