Flame moss is difficult the grow, definitely needs high lighting because mine died in my 33 aquarium where everything else is absolutely flourishing so that's my only warning. Unless you know it will do well, of course always great to give it a chance because it is a beautiful moss!
But my 3 gallon has a T8 fluorescent tube, the other one has an LED light clip which grows plants pretty well once they're acclimated to the water. There's a bunch of different ones if you look on Ebay, Amazon and wherever. They're good too because usually they bend so it can fit most places, the only thing then would be you wouldn't have a hood. You can get some plexi-glass or something if your really wanted to and get it cut to the shape of your 2.5
That's a bit much I know though.
Or you can use Saranwrap which is usually just a pain in the tushy.