There's a "hidden/unsupported" feature in MixEmergency 2.0 that allows you to create your own effects and transitions using Quartz Composer. To do this, you create a Quartz Composition, and place it in either: ~/Movies/MixEmergency/Plug-Ins/QCEffects/ or ~/Movies/MixEmergency/Plug-Ins/QCTransitions/
These Quartz Compositions can have the following keys used as inputs:
Image1 - The left channel (or current channel for effects) [type: image]
Image2 - The right channel (for transitions) [type: image]
Parameter1 - The first parameter [type: number]
Parameter2 - The second parameter (for effects) [type: number]
Mix - The crossfader mix position (for transitions) [type: number]
HoldChannel - (for transitions) [type: index] CutChannel - (for transitions) [type: index]
Here are a few example (and template) compositions: http://www.inklen.com/download/185/QCFXAndTransitions.zip
[Edit: just updated it with the correct paths.... whoops]
[Edit: added new example compositions]