I have a long-term non-trade receivable that I have calculated to NPV for and I am trying to figure out how to book the entry to reflect the difference between the face value of the long-term receivable and the net present value of the long-term receivable. I also am not sure what I need to book each month to off-set this difference. How would I go about doing that?

Why do you think you have to book the difference? Such differences are only booked when accounting for the diffences in valuation and then usually only as a balance day adjustment. The difference will have to be carried to a provision or reserve account with an amortisation account on the other side of the transaction