They could try a similar deal to the one Edward I gave to the Riccardi of Lucca. In return for giving him credit and loans on demand they recieved control over custom duties and in this way the Riccardi of Lucca could ensure that they regained their loses at a steady rate while the English King would remain in the black.
In such a deal revune raised by the government through taxes or whatever wouldn't effect the repayment of loans as that would be achieved through the buying and selling or mechandice under the control of the foreign banks who the Confederates borrowed from.
I wonder if that would work in the 19th century. How well did it work for the Riccardi?
And where, out of curiosity, did you read this? Not questioning your research, just that you seem to have done a bit of reading on Longshanks and I'd like to see if there are any good sources I should look for.