Well, I suppose we could restrict political donations, by limiting it to, say, $200 per registered voter.  Of course, to make it trackable, each voter has to have a unique ID number, like a SSN.

Additionally, to make up the bulk of the campaign funds, each taxpayer gets hit with an income tax surcharge, say .5%, the proceeds of which are deposited into a separate fund, independently managed.  It can be a non-government-runned trust fund.  This would be a requirement with no opt out by political candidates.

There would be details to work out, but it would greatly reduce the special interest monetary influence.