Actually I have found a way for at least the instrument plug ins to be accessed.
I was able to set up an instance of Sculpture in MS2 and record it in LE using Soundflower.
Route the audio from MainStage to Logic and record onto an audio track in Logic as follows:
If not already installed, get SoundFlower. After installing it.
A) Setup the sound you want in MS2 and audio output to Soundflower (remember to Apply Changes or it does not hold).
B) In Logic Express set the audio input to Soundflower and create a new audio track for recording. Important: set Soundflower's audio output to however you listen to your audio or you won't hear anything.
C) Press RECORD and start playing, LE captures Mainstage's sound.
I have not tried to wire LE's output to MS2 to take advantage of Space Designer. but since this functions, I'm not sure why that couldn't work as well. It is still flipping though a few screens though...might just be easier to get Logic Pro from the App store....