Two (I say two) fingers down on the pad and click for RMB. Much easier than using an actual second button, IMO. But I haven't tried it in Windows where you can also drag with RMB. Mac OS doesn't support RMB-drag (wish it did though).

All things considered, I'm quite surprised Apple hasn't done something about the singular button yet. Their Mighty Mouse has two buttons. Well, technically it has no buttons, but each side of the mouse clicks as either LMB or RMB. I wouldn't mind seeing a single button on under the pad but where you could configure clicking on the right side to be a different click than the left side.

I suppose you could also configure the button to be RMB-only and use the pad for LMB when tapped. Personally I hate pad-tapping, so I wouldn't consider than option for my own use.

The OS does support mice with pretty much any number of buttons (at least 9 or 10) if you want to use an external device.