It would be wise to do that in 2 UA awards.

1 - SFO-SIN-DPS-SIN-SFO
2 - SIN-MLE-SIN

or

1 - SFO-SIN-MLE-SIN-SFO
2 - SIN-DPS-SIN

The second award be nested within the first awards Stopover in SIN.
This seems the best value for miles. I know for a fact that the SFO-DPS-SFO will be 60/90/120k (Y/C/F) while the SIN-MLE-SIN should be 20/30/40k. So the total miles spend will be 80/120/160k (Y/C/F).