If you want to buy an individual bond or bill, then the T-Bill that'll be auctioned in January, 2019, would be a good fit. Of course you wouldn't buy it at auction, but you'd buy it strictly before your 55th birthday, preferably on December 1 (if that's a weekday and far enough in advance of your birthday), via the CPF Investment Scheme (SA), from whichever of the three primary dealers (DBS, UOB, OCBC) offers you the best price on that particular t-bill. I don't see any outstanding government bonds that would work as well, so that'll be the one.
Another choice, if you're willing to tolerate a slight amount of principal risk, is to use the Nikko AM Shenton Short Term Bond Fund (S$). You should buy that using a zero cost method -- I think Fundsupermart and POEMS are two such examples -- and also calculate any other costs/fees for quick redemption. It's helpful if your birthday falls right around the middle of the month -- December 15th or thereabouts -- since then you should be able to execute this maneuver with that particular fund within the same calendar month. I wouldn't cut it too close, though, especially on the purchase side.
You won't be able to shield S$40,000 of SA funds, please note. That's the required minimum. The CPF Investment Scheme (SA) is only for SA funds above S$40,000.