Had no problems doing this with overnight connections. Just ask, at the onset, to only be checked in as far as SIN, so they don't even pull a boarding pass/check you in for the SIN-SGN sector. [As distinct to only requesting your bags be tagged to SIN]. That way if you take a separate SIN-SGN flight, you will be a "no show" that no-one particularly has to worry about, vs a "fail to board" who they might page/chase before having to offload you.