A last resort (and yes I mean last): if all else fails and you're determined enough - things don't change, it's summer, no one up top listens, and someone can identify a qualified skills advisor (aka: coach, but don't call them that in front of people), and also a friendly faculty advisor if they are not the skill advisor. If they aren't, they should be ok with being just a liason/supervisor/supporter. "Club compeition acro & tumbling". Run it as a student club/activity like chess club, but cheer. Don't call yourselves "cheer" in front of administration, ever. Claim that you're different from "cheerleading" in that you want to provide an opportunity for girls to become familiar with the NCATA format (college prep, ya know?). There are no high school equivalents for NCATA, but claim that competitions come a close second if you need to justify them. Maybe enter a stunt group or two also, and have some people participate in the individual tumbling competitions. This route, you'll need all your ducks lined up and a minimum number of committed students when you approach the administration.
Drawbacks: you may have to take all comers. In that case you may still be able to form 2 squads for the "team" performance aspect. Finances may be hard, our state somewhat supported cheer as a sport, but I remember the pom squad (not a sport) was insanely expensive. Choosing a faculty advisor that you work well with that knows the ins and outs of funding a club activity would be an ideal situation here. Also, expect to butt heads with whatever remains of the existant cheer squad.