Hi,
I did this trick within the environment-layer of Logic-Audio as an extention of my "Virtual Maestro Tools" engine:
I am able now to mimick a multi-layer-crossfade-patch with the VSL-Legatos using CC11, note-velocity remapping and optionally CC-LP-filtering triggering the p-legatos on MIDI-Ch. "n" and the f-legatos on MIDI-channel "n+1". The advantage is, that I can use the Perf. Tool "as is", since both Legato-patches are getting triggered on the same port.
This works very well with all VS-standard legato-patches right out of the box. Just load the both dynamic-layers into succeeding MIDI-channels and handle the MW just like you would do it for EXP-patches. You have to vary the velocity-split-threshold (user-definable) a little from instrument to instrument. The only problem is, that legato-connections between both dynamic layers do not work, since the Perf.-Tool currently can't "link" the two MIDI-channels. To overcome this limitation, I started to simulate the Legato-processing within Logic itself. There was even no need to set up the Perf.-Tool properly then. You were recording finally processed lines then.
Pro: you are not stuck with a single port for the legato-patches.
Contra: Editing those final lines with keyswitches etc. is a little awkward.
Regards
Roman