40 odd years of history with the big seven only being a creation of the last 10 years or so, I find it funny that you think its not the JLA without them!
Cause...it's not. It's Justice League Detroit. Or, Justice League International. Or, Justice League Space Monkeys. It's not The JLA.
Firstly the big 7 that came about with Morrison is pure bullshit.
Wally and Kyle were not the "big" GL and Flash, thats Barry and Hal, whether you like em or not.
Oh jeez, here goes your normal "masturbatory semantics" about how great Hal Jordan is, and all that. The fact that Wally and Kyle aren't Barry and Hal has nothing to do with whether I consider them part of The Big Seven. It could be Bart and Guy behind the masks for all I care. If it's "The Flash" and "Green Lantern", then, that's that.
J'onn was a member for 5 minutes in the 60s, and didnt return til the late 80s.
I don't know the facts on that one. I was always under the assumption that he had been part of the League in many of its incarnations. Of course, that could just be some Post-Crisis remodeling that I didn't recognize. Still, he's definitely part of The Big Seven for me.
And quite frankly, ranking Aquaman above Hawkman, the Atom, Black Canary and Green Arrow is a joke!
Green Arrow, Black Canary, and Hawkman are cool enough. But, I'll always see them as second-string. The Atom? Boring. Aquaman? I don't need to make a joke here. It's understood.
The concept of the big seven is laughable!
No, YOU are!
Fuck, Red Tornado had more claim to being in that line up than J'onn!
Someone's got their nerd-panties in a wad...

P.S. Red Tornado is lame, lamer, lamest. J'onn rules. Manchester United rocks, and The Spice Girls are the UK's greatest claim to fame. Eat it, poof!
But see, this is where your argument falls down.
Not everyone who goes to see this is gonna be oblivious to the history, and some of them, wanting to revisit their youth, wont gove two fucks about Martian Manhunter because he wasnt a big character!
You say the likes of Hawkman, Atom and Green Arrow are all second tier, but you see J'onn as top tier?
The guy didnt even have his own book until the Morrison run (discounting two mini-series), at least Hawkman and Atom both had their own books at several times in their careers.
They also happen to have golden age heritage!
J'onn was a backup character in Detective Comics, and vanished in the early 60s.
Apart from the odd cameo appearance, he didnt resurace again until JL Detroit in the mid to late 80s.
By that time, characters like GA, Aquaman, Hawkman and Atom had all become far more well known that him.
In fact, even non-comic readers would have known them because of the Super Friends cartoon.
Also, you have to remember that of from the mid 80s, up to the Doomsday era of the mid 90s, the only character excluding J'onn, to have an almost consistant prescence in the League was Batman.
Superman only rejoined in the lead up to Doomsday.
Wonder Woman briefly joined JLE, then disapeared, only to show up in JLA a little while before it was cancelled.
Hal briefly lead the JLE, and Wally didnt join until the first issue of JLE.
Of course there was some GL prescence in this era with Guy, but even he ended up with no GL ring!
That was pretty much a decade without a "the big seven".
That was also the decade that J'onn suddenly became the heart and soul of the team, which to a long term reader, was forced, and made no sense!
Nobody here is saying it has to be a team made up of Blue Beetle, Booster Gold, Firestorm, Zatanna & Elongated Man (those last two, like Red Tornado have much more of a history with the JLA than J'onn), but I think there is enough recognition with characters through comic books, old Super Friends cartoons & newer JLA cartoons, that a movie can survive without Superman & Batman!
As long as GL, Flash, Wonderwoman & maybe Aquaman are present, you can slip in Hawkman, Hawkwoman, Atom, Green Arrow, Black Canary & a few others, and enough people will recognise them!
I'm also willing to bet, that theres also a lot of people out there who would see a superhero film called JLA even though they have no idea who any of the members were, just like many people who saw X-Men had no idea who any of the members were before they saw it.
All they were going to see was an action film.
People might know Batman & Superman, but that doesnt mean they know they are in a superteam called JLA!
The big seven is a fanboy dream!