Yes, report the "Cost or other basis" in Form 1099-B Box 1e, even though it's not reported by the brokerage firm (this is common).
Since you know the basis for the stock, enter it when you are entering the rest of the 1099-B information - in the interview menu for Stocks, Mutual Funds, Bonds and Other.
The IRS will be looking for that 1099-B in your return, to ensure you report the "Proceeds" from the sale. Adding the "cost or Other Basis" information will ensure you are only taxed on your gain. Adding missing cost basis information will not create a "mismatch" with the IRS record of the 1099-B.
