Normally 4 sec shuttle speed is ok when shooting @ Marina Bay since the sky up there is a bit limited.
Anymore and you might have overlapping fireworks which might make your pictures whiteout.
Anyway, I use bulb mode with my right hand and left hand as my black card...
Ok, hand not black but still workable.
Here's a sample using the above mentioned method for your preview.
http://www.clubsnap.com/forums/showthread.php?t=813854