SIN-KUL is practically a commuter route for some.. such that there are two options to achieve this.. you can either reserve a seat in advance and pay the walkup price (same fare across all airlines).. or for less $$, you can go standby on the flights. There's a waiting area .. you have a numbered ticket.. and depending on when you get there, it could be a short or long wait. No mileage accrual on the standby fares, of course.

Fares are cheaper from KUL-SIN instead of vv, due to exchange rates.

Now that you mentioned it, I am also considering a KL daytrip. Things are so cheap there.. and the new rail link from the airport is a godsend. Anything to avoid those touts.