I think this would prove to be exceedingly difficult in practice. In fact, this kind of is the system we live under, and it doesn't work.

Sure, you could argue for changes in the amounts, and who can donate to what, but consider this: I believe Obama's biggest corporate donor in 2008 was Goldman Sachs, and the value of their contribution was on the order of $1,000,000 (correct me if I'm wrong). Considering the funds that Goldman Sachs has access to, and the cost of a Presidential campaign, this is a pittance.

Clearly there are other forces at work here. You can fiddle with the numbers, but I don't know how you set up a system that doesn't reward "cheaters" or the already wealthy (ie received their "contributions" in advance). Which is where we're at.