I've played a few games with them and it's mostly subtle changes unless you want to ally forces in.
My original list was Isildur, 2 captains and 12 each of spear, shield and bows.
The variations you can take are in giving the captains shields and the heroes horses for the cost of a few troops, which I think is worth it. It doesn't seem like much but it can be more than you think.
I also think that taking a banner for this force is a must.
If i was going to take Numenor to a tournament I would playtest with Isildur & co and some Knights of Minas Tirith
Here's a few lists: 500 pts
Isildur, 2 Captains & 12 of each warrior (spear/shield, shield & bow)
Isildur & 2 Captains, all mounted & 14 Shield, 14 spears, 1 additional man with banner. Swap out the 2 captains horses to give the banner a spear and get 1 extra troop.
Isildur, 1 Captain both with horses, 10 shields & 10 spear & shield,
Ally 1 captain of MT with horse, lance & 6 knights with shield
You aren't going to get the most competitive army, but they will still put up a good brawl. The banner would be nice to have on the last list, but I cant seem to fit it in in a way I like at the moment.
Isildur is the core of the force as he needs to put the ring on and take down the enemy threats that will kill your troops.
The troops are really just there to be a swarm army - unfortunately their stat's are in all the wrong places to fight well against a conventional army. Shield with some when you need to and try not to lose the spears.
The knights I see as Isildurs bodyguard (FOTR intro) so they are still thematic to me and offer a pretty good punch, especially with the lances.
If you want to stay pure on the theme, you could take citadel guard mounted instead as they no doubt would have been around.
I hope that gives you a bit of an insight. Otherwise all I can think of is using the captains for heroic combats to try and break them quickly. There is nothing wrong with him beating you in his first game, losing is what puts people off, so don't be afraid of giving it a go, he might enjoy it so much that he wants to face you again when using a better army
One last thing, I would probably feint as much as possible, but not give up the higher FV. You really need to do wounds with this army or you will break quickly.