Hi Luthier,
You can build a version of it yourself, it isn't hard and only takes a handful of parts, it's nothing but two simple emitter follower buffers. The ESPE01 uses FETs but I rather doubt that there is much difference between them in terms of behavior.
Installation on the Big Briar Etherwave isn't too hard either, though it is a bit more involved than the later Etherwave Standard and Plus. I actually did this a while back and documented it here:
http://www.thereminworld.com/forums/T/28485?post=213553#213553
You might want to download the sound file there to experience directly how the mod influences the bass end of things, you may or may not like the change it introduces in the tone. It does make the bass end easier to play though.
If you are new to the Etherwave in general I would recommend you play it for a while before modding it, just so you are familiar with what you are changing. Though you can more or less jumper out my version of the buffer if it turns out it isn't what you wanted. You might also play around with limited coupling to try to get the best of both worlds (I haven't experimented along these lines at all).