@AC Schnitzer: Wow, I can tell that you're a very keen aviator! Glad that you tried Flight Experience. Man, I should have tried more adventurous stuff like your engine failure when I went there last time. :P
SIA's cadet pilot recruitment page says the following:
[...] you must have obtained a minimum of 5 Credits in the GCE ‘O’ level or its equivalent. These must include English, Mathematics and a Science subject, preferably Physics, taken at one sitting.
Do you have another Science subject other than Physics? If so you might be meeting the minimum requirements. Maybe you want to consider calling the HR to clarify?
Anyway, I can't say much for HR, but if I were you and if I can afford it, I'd probably do the same and take the O Levels just to be sure that I meet the minimum requirements, while waiting for the economy to recover (hopefully some time next year). But if I'm not mistaken this year's O Levels registration has been closed, hasn't it?
As for the CPL... I'm not sure if SIA's policy accepts CPL holder and above or not for cadet pilots. I seem to recall that some airlines have a policy of not accepting CPL holders and above as cadet pilots.
Wishing you all the best!