To start, the "99%" demographic is imaginary. There is no such group. Most Americans do not see the world as a contest between the masses and a tiny oligarchy.
If whatever special interest it is with which you are identifying wishes to get into the lobbying business, however, then it has to hire lobbyists just like every other pressure group does. Influencing government today takes money, access, money, information, money, a law drafting department, money, wining and dining, money, reelection assistance, money ... well, you get the picture. The way to begin is to organize as a nonprofit corporation and raise a big pool of funding. Doing that, of course, would transform you into what you see as the enemy. The alternative is hit the streets, just as the Occupiers are now doing, which is to say to transform yourself into a camera-ready tool of associated politicians who are running for reelection and getting their money, and guidance, from others.
Good luck. You'll need it.