Calculate the accrued interest on the bond, add it onto the price. Calculate the remaining periods but be very specific and go into decimal places to be more precise. I didnt check the guide posted but i assume thats what it says.
Apparently BA II Plus has two options - annual or semiannual coupons. So you enter into BOND mode, choose semiannual option, specify the contract initiation date and the bond maturity date ( as proper dates) and it calculates whole coupons as well as the first fractional coupon. Quite neat, except it becomes obsolete when you have quarterly or any other periodicity. Excel all the way.