I actually think it would be cool to introduce them without being obvious. Make it a goddamn surprise for once.
Like...maybe te Avengers need to go into space, so they contact this "private militia" off of an island near California that has advanced tech and the training to use it. Their disciplined leader flies the jet, with his blonde woman acting as the cold businesswoman. Sprinkle in other X-men as the crew, using image inducers as an excuse when necessary. Wolverine is not present, but has already been sent to infiltrate the destination to gather Intel. His presence is background information that can only be gleaned by paying attention to things the "crew" say.
Wait till shit hits the fan, then you pull the Whedon-style Cyclops unleashes the punch dimension on some poor alien, big crew guy turns metal, yadayada, in a sewer nearby three claws extend in the face of an alien horde
Terrible fanfiction, I know. But a man can dream
