I have an HP Envy Touchsmart 15 and I can't find a way to emulate a right click on a touchscreen. I remember there being an option for it in way older versions of Ubuntu, as to hold the left click button for so long and it'd emulate a right click. However in 13.10 I cannot find any such option under any accessibility or mouse settings.
It looks like Ubuntu Unity currently only supports 3/4 finger touch gestures https://wiki.ubuntu.com/Multitouch and only on a limited number of screen devices https://wiki.ubuntu.com/Multitouch/HardwareSupport...
However, it is suggested you can use Ginn to define custom gestures. See How to support right-click in Ginn on https://wiki.ubuntu.com/Multitouch/Ginn (it's not much of an instruction but it indicates it should be possible...)