There are two issues you'll need to contend with.

The first is SQ making award tickets available in your desired class. SQ has a reputation for being tight with premium cabin seats. If you go to the *A or UA forums, and search for "ANA tool", you'll find instructions on how to search for ticket availability on non-CO *A carriers.

The second issue with using SQ to go to India from IAH is that there's a long layover in SIN between the arrival of the flight from IAH and the first bank of departures for India. You might find yourself preferring LH or CO flights based on schedule.