Incrementally, via Lessig's plan. The thing about campaign finance is that it can actually be reformed piecemeal and by external efforts simply be putting enough money in the right place and the right time. Well, not that simply, but close enough.

The current people in Congress were elected under the current system and thus must be at least slightly wary of a different system. Despite this, there is some support in Congress for these sorts of reform. Perhaps those who support it do so because they think it is the right thing to do, perhaps merely because they think they can do well under the new system.

But you don't have to change the campaign finance rules to start with. By concentrating money in a few places on a single issue, i.e. using the current system, you can elect or help elect members favorable to the new system. If that works, you kick it up a notch and try to get more elected. At some point it's either going to peter out or it's going to have some sort of permanent success.

This is not to imply that it's a walk in the park, but there is a road to success here. Trying to effect significant change on other issues which run counter to big money seems to me to be less realistic, but that's just my opinion.