Only if the sale of the receivables is sold without recourse should you add it back.
If the job of hounding down the receivables still remains with the selling firm, the receivables should be added back to the balance sheet for analysis purposes. Basically by selling receivables for which you're still liable is just a collateralized loam; you're taking the revenues from the receivables and using it to pay the "lender" payments on the "sale". By doing this you're now the servicer of the loan.
This is simliar to how Countrywide runs their operations by selling off their loan portfolios to Fannie Mae and Freddie Mac who repackages them into MBS's.
I forget, however, how you account for the interest on the loan and any loss you take on the a/r. Is the interest calculated by the loss you take on the loan and then amortized as an interest expense?