The proposed solution is to expand what it means to be a bank. The new banking function is to create and combine different ways to create money.
Below is a Flash mockup I made of a Payment Spectrum user interface, complete with details, demos and "user stories".
You can explore the features and possibilities and perhaps think up a few of your own.
While being a bank would be useful, it is not essential to setting up such a Payment Spectrum. Only a bank account would be needed.