1. Start anti-corporate political advertising and lobbying groups. They would boycott any corporation (and their products) that spends more than $1,000 / year on political advertising or lobbying. A list of such companies and the money involved would be posted on a dedicated website.
2. Any stockholder of these companies can claim that spending money lobbying for things that do not directly benefit the stockholders of the company is in violation of in every state and could be punished for damages (probably up to 3 times the $ value of the expenditures) in any State or Federal court.
These two simple actions will stop excessive corporate spending on political lobbying almost overnight.