You could possibly do it with another keyboard synth or Midi controller by altering the envelopes for attack-sustain-decay either on the keyboard synth or in the soft synth. Possibly you could the same with a split keyboard depending on the capabilities of the unit.

As a piano teacher you probably have a dog-eared (and possibly much hated) copy of Hanon's Virtuoso Pianist in 60 exersizes laying about.
 
These are great on the organ.  Bust out one of these exercises with both hands going at top speed and insta Jon Lord. Page McConnell of Phish also swears by Hanon for really improving his organ playing.
 
That said, Hanon can be pretty aganozing. The name causes me to roll on the floor convulsing.

I'm really the last person who should recommend Hanon. One summer I vowed to make it through all 60 exercises. I made it through about six  -- poorly.
 
In university we had a Hanon competition as part of a fund raiser (you can imagine the millions we raked in). Basically it was bunch of music studens showing off how fast they can rip through Hanon.
 
I made it through one, blew the second one spectacularily, and played my self off with a couple of bars of the Entertainer. I never played Hanon again.
 
One of my professors sight read the the exercises off an overhead projector which is still one of the most riduculous musical stunt performances I have witnessed.

Our performance may have been hindered by the fact we had been drinking before hand :)

Maybe that's why that guy in church was so good.  I always wondered about him!  lol

I'd just like to report that the B4 does respond to the sustain pedal.

This is on the B4 first version.

If the sustain is sent only via the channel of the lower manual (Ch-2 in this case), the upper manual is independent of the sustain.

I have not tested the other channels it uses (ch1 and ch3), but for other things sending to ch-1 spreads to all 3 channels, while sending to ch-2 and ch-3 act independently, a feature that can and I do put to some use.

So, this means that the sustain can even be sent to the pedals independently, if so any one wanted to do.

The B4-II might be the same, but those who use the B4-II can check if they need to or want-to.

Also, using the sustain with the B4 does have some interesting uses, including the fact that the expression pedal is independent of the sustain. This means that a sustained note can be swelled up or down after released.

Just sharing info, in case, and as was asked early in this thread.